builtins: Select correct code fragments when compiling for Thumb1/Thum2/ARM ISA.

Summary:
Value of __ARM_ARCH_ISA_THUMB isn't based on the actual compilation
mode (-mthumb, -marm), it reflect's capability of given CPU.

Due to this:
 - use  __tbumb__ and __thumb2__ insteand of __ARM_ARCH_ISA_THUMB
 - use '.thumb' directive consistently  in all affected files
 - decorate all thumb functions using
   DEFINE_COMPILERRT_THUMB_FUNCTION()

---------
Note: This patch doesn't fix broken Thumb1 variant of __udivsi3 !

Reviewers: weimingz, rengolin, compnerd

Subscribers: aemerson, dim

Differential Revision: https://reviews.llvm.org/D30938

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@298713 91177308-0d34-0410-b5e6-96231b3b80d8

14 files changed, 108 insertions, 64 deletions

diff --git a/lib/builtins/arm/aeabi_idivmod.S b/lib/builtins/arm/aeabi_idivmod.S
index 0164b15dc..4419929f6 100644
--- a/lib/builtins/arm/aeabi_idivmod.S
+++ b/lib/builtins/arm/aeabi_idivmod.S
@@ -20,16 +20,25 @@
 #endif
 
         .syntax unified
+        .syntax unified
+        .text
+#if defined(USE_THUMB_PROLOGUE)
+        .thumb
+#endif
         .p2align 2
+#if defined(USE_THUMB_PROLOGUE)
+DEFINE_COMPILERRT_THUMB_FUNCTION(__aeabi_idivmod)
+#else
 DEFINE_COMPILERRT_FUNCTION(__aeabi_idivmod)
-#if __ARM_ARCH_ISA_THUMB == 1
+#endif
+#if defined(USE_THUMB_1)
         push    {r0, r1, lr}
         bl      SYMBOL_NAME(__divsi3)
         pop     {r1, r2, r3} // now r0 = quot, r1 = num, r2 = denom
         muls    r2, r0, r2   // r2 = quot * denom
         subs    r1, r1, r2
         JMP     (r3)
-#else
+#else  // defined(USE_THUMB_1)
         push    { lr }
         sub     sp, sp, #4
         mov     r2, sp
@@ -42,7 +51,7 @@ DEFINE_COMPILERRT_FUNCTION(__aeabi_idivmod)
         ldr     r1, [sp]
         add     sp, sp, #4
         pop     { pc }
-#endif // __ARM_ARCH_ISA_THUMB == 1
+#endif //  defined(USE_THUMB_1)
 END_COMPILERRT_FUNCTION(__aeabi_idivmod)
 
 NO_EXEC_STACK_DIRECTIVE
diff --git a/lib/builtins/arm/aeabi_uidivmod.S b/lib/builtins/arm/aeabi_uidivmod.S
index a627fc740..37dae4a10 100644
--- a/lib/builtins/arm/aeabi_uidivmod.S
+++ b/lib/builtins/arm/aeabi_uidivmod.S
@@ -21,8 +21,16 @@
 #endif
 
         .syntax unified
+        .text
+#if defined(USE_THUMB_PROLOGUE)
+        .thumb
+#endif
         .p2align 2
+#if defined(USE_THUMB_PROLOGUE)
+DEFINE_COMPILERRT_THUMB_FUNCTION(__aeabi_uidivmod)
+#else
 DEFINE_COMPILERRT_FUNCTION(__aeabi_uidivmod)
+#endif
 #if __ARM_ARCH_ISA_THUMB == 1
         cmp     r0, r1
         bcc     LOCAL_LABEL(case_denom_larger)
diff --git a/lib/builtins/arm/bswapdi2.S b/lib/builtins/arm/bswapdi2.S
index fb226cea2..4e5a579cf 100644
--- a/lib/builtins/arm/bswapdi2.S
+++ b/lib/builtins/arm/bswapdi2.S
@@ -11,7 +11,7 @@
 
 	.syntax unified
 	.text
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 	.thumb
 #endif
 
@@ -21,7 +21,7 @@
 // Reverse all the bytes in a 64-bit integer.
 //
 	.p2align 2
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 DEFINE_COMPILERRT_THUMB_FUNCTION(__bswapdi2)
 #else
 DEFINE_COMPILERRT_FUNCTION(__bswapdi2)
diff --git a/lib/builtins/arm/bswapsi2.S b/lib/builtins/arm/bswapsi2.S
index 553c3c2e3..60342ae0f 100644
--- a/lib/builtins/arm/bswapsi2.S
+++ b/lib/builtins/arm/bswapsi2.S
@@ -11,7 +11,7 @@
 
 	.syntax unified
 	.text
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 	.thumb
 #endif
 
@@ -21,7 +21,7 @@
 // Reverse all the bytes in a 32-bit integer.
 //
 	.p2align 2
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 DEFINE_COMPILERRT_THUMB_FUNCTION(__bswapsi2)
 #else
 DEFINE_COMPILERRT_FUNCTION(__bswapsi2)
diff --git a/lib/builtins/arm/clzdi2.S b/lib/builtins/arm/clzdi2.S
index 6068c176f..fe56a183f 100644
--- a/lib/builtins/arm/clzdi2.S
+++ b/lib/builtins/arm/clzdi2.S
@@ -15,13 +15,13 @@
 
 	.syntax unified
 	.text
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 	.thumb
 #endif
 
 
 	.p2align	2
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 DEFINE_COMPILERRT_THUMB_FUNCTION(__clzdi2)
 #else
 DEFINE_COMPILERRT_FUNCTION(__clzdi2)
diff --git a/lib/builtins/arm/clzsi2.S b/lib/builtins/arm/clzsi2.S
index c2ba3a8cf..28d43041e 100644
--- a/lib/builtins/arm/clzsi2.S
+++ b/lib/builtins/arm/clzsi2.S
@@ -15,12 +15,12 @@
 
 	.syntax unified
 	.text
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 	.thumb
 #endif
 
 	.p2align	2
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 DEFINE_COMPILERRT_THUMB_FUNCTION(__clzsi2)
 #else
 DEFINE_COMPILERRT_FUNCTION(__clzsi2)
diff --git a/lib/builtins/arm/comparesf2.S b/lib/builtins/arm/comparesf2.S
index ef7091bf3..1f7031cbf 100644
--- a/lib/builtins/arm/comparesf2.S
+++ b/lib/builtins/arm/comparesf2.S
@@ -38,15 +38,20 @@
 //===----------------------------------------------------------------------===//
 
 #include "../assembly.h"
-.syntax unified
-#if __ARM_ARCH_ISA_THUMB == 2
-.thumb
+    .syntax unified
+    .text
+#if defined(USE_THUMB_PROLOGUE)
+    .thumb
 #endif
 
 @ int __eqsf2(float a, float b)
 
     .p2align 2
+#if defined(USE_THUMB_PROLOGUE)
+DEFINE_COMPILERRT_THUMB_FUNCTION(__eqsf2)
+#else
 DEFINE_COMPILERRT_FUNCTION(__eqsf2)
+#endif
 #if defined(COMPILER_RT_ARMHF_TARGET)
     vmov r0, s0
     vmov r1, s1
@@ -67,7 +72,7 @@ DEFINE_COMPILERRT_FUNCTION(__eqsf2)
     // flag if both a and b are zero (of either sign).  The shift of r3 doesn't
     // effect this at all, but it *does* make sure that the C flag is clear for
     // the subsequent operations.
-#if __ARM_ARCH_ISA_THUMB == 1
+#if defined(USE_THUMB_1)
     lsrs    r6,     r3, #1
     orrs    r6,     r2
 #else
@@ -75,7 +80,7 @@ DEFINE_COMPILERRT_FUNCTION(__eqsf2)
 #endif
     // Next, we check if a and b have the same or different signs.  If they have
     // opposite signs, this eor will set the N flag.
-#if __ARM_ARCH_ISA_THUMB == 1
+#if defined(USE_THUMB_1)
     beq     1f
     movs    r6,     r0
     eors    r6,     r1
@@ -89,7 +94,7 @@ DEFINE_COMPILERRT_FUNCTION(__eqsf2)
     // ignoring NaNs for now), this subtract will zero out r0.  If they have the
     // same sign, the flags are updated as they would be for a comparison of the
     // absolute values of a and b.
-#if __ARM_ARCH_ISA_THUMB == 1
+#if defined(USE_THUMB_1)
     bmi     1f
     subs    r0,     r2, r3
 1:
@@ -108,7 +113,7 @@ DEFINE_COMPILERRT_FUNCTION(__eqsf2)
     // still clear from the shift argument in orrs; if a is positive and b
     // negative, this places 0 in r0; if a is negative and b positive, -1 is
     // placed in r0.
-#if __ARM_ARCH_ISA_THUMB == 1
+#if defined(USE_THUMB_1)
     bhs     1f
     // Here if a and b have the same sign and absA < absB, the result is thus
     // b < 0 ? 1 : -1. Same if a and b have the opposite sign (ignoring Nan).
@@ -127,7 +132,7 @@ DEFINE_COMPILERRT_FUNCTION(__eqsf2)
     // the sign of b in r0.  Thus, if both are negative and a < b, -1 is placed
     // in r0, which is the desired result.  Conversely, if both are positive
     // and a > b, zero is placed in r0.
-#if __ARM_ARCH_ISA_THUMB == 1
+#if defined(USE_THUMB_1)
     bls     1f
     // Here both have the same sign and absA > absB.
     movs    r0,         #1
@@ -145,14 +150,14 @@ DEFINE_COMPILERRT_FUNCTION(__eqsf2)
     // If a == b, then the Z flag is set, so we can get the correct final value
     // into r0 by simply or'ing with 1 if Z is clear.
     // For Thumb-1, r0 contains -1 if a < b, 0 if a > b and 0 if a == b.
-#if __ARM_ARCH_ISA_THUMB != 1
+#if defined(USE_THUMB_1)
     it ne
     orrne   r0,     r0, #1
 #endif
 
     // Finally, we need to deal with NaNs.  If either argument is NaN, replace
     // the value in r0 with 1.
-#if __ARM_ARCH_ISA_THUMB == 1
+#if defined(USE_THUMB_1)
 LOCAL_LABEL(CHECK_NAN):
     movs    r6,         #0xff
     lsls    r6,         #24
@@ -180,7 +185,11 @@ DEFINE_COMPILERRT_FUNCTION_ALIAS(__nesf2, __eqsf2)
 @ int __gtsf2(float a, float b)
 
     .p2align 2
+#if defined(USE_THUMB)
+DEFINE_COMPILERRT_THUMB_FUNCTION(__gtsf2)
+#else
 DEFINE_COMPILERRT_FUNCTION(__gtsf2)
+#endif
     // Identical to the preceding except in that we return -1 for NaN values.
     // Given that the two paths share so much code, one might be tempted to
     // unify them; however, the extra code needed to do so makes the code size
@@ -189,7 +198,7 @@ DEFINE_COMPILERRT_FUNCTION(__gtsf2)
     vmov r0, s0
     vmov r1, s1
 #endif
-#if __ARM_ARCH_ISA_THUMB == 1
+#if defined(USE_THUMB_1)
     push    {r6, lr}
     lsls    r2,        r0, #1
     lsls    r3,        r1, #1
@@ -254,7 +263,12 @@ DEFINE_COMPILERRT_FUNCTION_ALIAS(__gesf2, __gtsf2)
 @ int __unordsf2(float a, float b)
 
     .p2align 2
+#if defined(USE_THUMB)
+DEFINE_COMPILERRT_THUMB_FUNCTION(__unordsf2)
+#else
 DEFINE_COMPILERRT_FUNCTION(__unordsf2)
+#endif
+
 #if defined(COMPILER_RT_ARMHF_TARGET)
     vmov    r0,         s0
     vmov    r1,         s1
@@ -263,7 +277,7 @@ DEFINE_COMPILERRT_FUNCTION(__unordsf2)
     lsls    r2,         r0, #1
     lsls    r3,         r1, #1
     movs    r0,         #0
-#if __ARM_ARCH_ISA_THUMB == 1
+#if defined(USE_THUMB_1)
     movs    r1,         #0xff
     lsls    r1,         #24
     cmp     r2,         r1
diff --git a/lib/builtins/arm/divmodsi4.S b/lib/builtins/arm/divmodsi4.S
index 999c310ec..3c8359852 100644
--- a/lib/builtins/arm/divmodsi4.S
+++ b/lib/builtins/arm/divmodsi4.S
@@ -23,7 +23,7 @@
 
 	.syntax unified
 	.text
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 	.thumb
 #endif
 
@@ -32,7 +32,7 @@
 @   value is the quotient, the remainder is placed in the variable.
 
 	.p2align 3
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 DEFINE_COMPILERRT_THUMB_FUNCTION(__divmodsi4)
 #else
 DEFINE_COMPILERRT_FUNCTION(__divmodsi4)
diff --git a/lib/builtins/arm/divsi3.S b/lib/builtins/arm/divsi3.S
index f066f60ad..ad96c9e5b 100644
--- a/lib/builtins/arm/divsi3.S
+++ b/lib/builtins/arm/divsi3.S
@@ -20,10 +20,10 @@
 #define CLEAR_FRAME_AND_RETURN \
     pop    {r4, r7, pc}
 
-	.syntax unified
-	.text
-#if __ARM_ARCH_ISA_THUMB == 2
-	.thumb
+   .syntax unified
+   .text
+#if defined(USE_THUMB_PROLOGUE)
+   .thumb
 #endif
 
 	.p2align 3
@@ -33,7 +33,7 @@ DEFINE_AEABI_FUNCTION_ALIAS(__aeabi_idiv, __divsi3)
 @ int __divsi3(int divident, int divisor)
 @   Calculate and return the quotient of the (signed) division.
 
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 DEFINE_COMPILERRT_THUMB_FUNCTION(__divsi3)
 #else
 DEFINE_COMPILERRT_FUNCTION(__divsi3)
@@ -72,7 +72,7 @@ ESTABLISH_FRAME
 //  abs(a) / abs(b)
     bl      SYMBOL_NAME(__udivsi3)
 //  Apply sign of quotient to result and return.
-#  if __ARM_ARCH_ISA_THUMB == 1
+#  if defined(USE_THUMB_1)
     asrs    r4,     #31
     eors    r0,     r4
     subs    r0,     r0, r4
diff --git a/lib/builtins/arm/modsi3.S b/lib/builtins/arm/modsi3.S
index 1d302edc6..0986d8494 100644
--- a/lib/builtins/arm/modsi3.S
+++ b/lib/builtins/arm/modsi3.S
@@ -22,7 +22,7 @@
 
 	.syntax unified
 	.text
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 	.thumb
 #endif
 
@@ -30,7 +30,7 @@
 @   Calculate and return the remainder of the (signed) division.
 
 	.p2align 3
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 DEFINE_COMPILERRT_THUMB_FUNCTION(__modsi3)
 #else
 DEFINE_COMPILERRT_FUNCTION(__modsi3)
diff --git a/lib/builtins/arm/udivmodsi4.S b/lib/builtins/arm/udivmodsi4.S
index 1ad8ee34b..860fced63 100644
--- a/lib/builtins/arm/udivmodsi4.S
+++ b/lib/builtins/arm/udivmodsi4.S
@@ -16,8 +16,7 @@
 
 	.syntax unified
 	.text
-
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 	.thumb
 #endif
 
@@ -27,7 +26,7 @@
 @   value is the quotient, the remainder is placed in the variable.
 
 	.p2align 2
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 DEFINE_COMPILERRT_THUMB_FUNCTION(__udivmodsi4)
 #else
 DEFINE_COMPILERRT_FUNCTION(__udivmodsi4)
@@ -67,7 +66,7 @@ DEFINE_COMPILERRT_FUNCTION(__udivmodsi4)
 	clz	r3, r1
 	/* r0 >= r1 implies clz(r0) <= clz(r1), so ip <= r3. */
 	sub	r3, r3, ip
-#    if __ARM_ARCH_ISA_THUMB == 2
+#    if defined(USE_THUMB_2)
 	adr	ip, LOCAL_LABEL(div0block) + 1
 	sub	ip, ip, r3, lsl #1
 #    else
@@ -78,7 +77,7 @@ DEFINE_COMPILERRT_FUNCTION(__udivmodsi4)
 	mov	r3, #0
 	bx	ip
 #  else
-#    if __ARM_ARCH_ISA_THUMB == 2
+#    if defined(USE_THUMB_2)
 #    error THUMB mode requires CLZ or UDIV
 #    endif
 	str	r4, [sp, #-8]!
diff --git a/lib/builtins/arm/udivsi3.S b/lib/builtins/arm/udivsi3.S
index fcc472b4f..2a0209927 100644
--- a/lib/builtins/arm/udivsi3.S
+++ b/lib/builtins/arm/udivsi3.S
@@ -16,8 +16,7 @@
 
 	.syntax unified
 	.text
-
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 	.thumb
 #endif
 
@@ -27,7 +26,7 @@ DEFINE_AEABI_FUNCTION_ALIAS(__aeabi_uidiv, __udivsi3)
 @ unsigned int __udivsi3(unsigned int divident, unsigned int divisor)
 @   Calculate and return the quotient of the (unsigned) division.
 
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 DEFINE_COMPILERRT_THUMB_FUNCTION(__udivsi3)
 #else
 DEFINE_COMPILERRT_FUNCTION(__udivsi3)
@@ -40,7 +39,7 @@ DEFINE_COMPILERRT_FUNCTION(__udivsi3)
 #else
 	cmp	r1, #1
 	bcc	LOCAL_LABEL(divby0)
-#if __ARM_ARCH_ISA_THUMB == 1
+#if defined(USE_THUMB_1)
 	bne LOCAL_LABEL(num_neq_denom)
 	JMP(lr)
 LOCAL_LABEL(num_neq_denom):
@@ -49,7 +48,7 @@ LOCAL_LABEL(num_neq_denom):
 	JMPc(lr, eq)
 #endif
 	cmp	r0, r1
-#if __ARM_ARCH_ISA_THUMB == 1
+#if defined(USE_THUMB_1)
 	bhs LOCAL_LABEL(num_ge_denom)
 	movs r0, #0
 	JMP(lr)
@@ -81,7 +80,7 @@ LOCAL_LABEL(num_ge_denom):
 	clz	r3, r1
 	/* r0 >= r1 implies clz(r0) <= clz(r1), so ip <= r3. */
 	sub	r3, r3, ip
-#    if __ARM_ARCH_ISA_THUMB == 2
+#    if defined(USE_THUMB_2)
 	adr	ip, LOCAL_LABEL(div0block) + 1
 	sub	ip, ip, r3, lsl #1
 #    else
@@ -92,17 +91,17 @@ LOCAL_LABEL(num_ge_denom):
 	mov	r3, #0
 	bx	ip
 #  else /* No CLZ Feature */
-#    if __ARM_ARCH_ISA_THUMB == 2
+#    if defined(USE_THUMB_2)
 #    error THUMB mode requires CLZ or UDIV
 #    endif
-#    if __ARM_ARCH_ISA_THUMB == 1
+#    if defined(USE_THUMB_1)
 #      define BLOCK_SIZE 10
 #    else
 #      define BLOCK_SIZE 12
 #    endif
 
 	mov	r2, r0
-#    if __ARM_ARCH_ISA_THUMB == 1
+#    if defined(USE_THUMB_1)
 	mov ip, r0
 	adr r0, LOCAL_LABEL(div0block)
 	adds r0, #1
@@ -111,7 +110,7 @@ LOCAL_LABEL(num_ge_denom):
 #    endif
 	lsrs	r3, r2, #16
 	cmp	r3, r1
-#    if __ARM_ARCH_ISA_THUMB == 1
+#    if defined(USE_THUMB_1)
 	blo LOCAL_LABEL(skip_16)
 	movs r2, r3
 	subs r0, r0, #(16 * BLOCK_SIZE)
@@ -123,7 +122,7 @@ LOCAL_LABEL(skip_16):
 
 	lsrs	r3, r2, #8
 	cmp	r3, r1
-#    if __ARM_ARCH_ISA_THUMB == 1
+#    if defined(USE_THUMB_1)
 	blo LOCAL_LABEL(skip_8)
 	movs r2, r3
 	subs r0, r0, #(8 * BLOCK_SIZE)
@@ -135,7 +134,7 @@ LOCAL_LABEL(skip_8):
 
 	lsrs	r3, r2, #4
 	cmp	r3, r1
-#    if __ARM_ARCH_ISA_THUMB == 1
+#    if defined(USE_THUMB_1)
 	blo LOCAL_LABEL(skip_4)
 	movs r2, r3
 	subs r0, r0, #(4 * BLOCK_SIZE)
@@ -147,7 +146,7 @@ LOCAL_LABEL(skip_4):
 
 	lsrs	r3, r2, #2
 	cmp	r3, r1
-#    if __ARM_ARCH_ISA_THUMB == 1
+#    if defined(USE_THUMB_1)
 	blo LOCAL_LABEL(skip_2)
 	movs r2, r3
 	subs r0, r0, #(2 * BLOCK_SIZE)
@@ -158,7 +157,7 @@ LOCAL_LABEL(skip_2):
 #    endif
 
 	/* Last block, no need to update r2 or r3. */
-#    if __ARM_ARCH_ISA_THUMB == 1
+#    if defined(USE_THUMB_1)
 	lsrs r3, r2, #1
 	cmp r3, r1
 	blo LOCAL_LABEL(skip_1)
@@ -191,7 +190,7 @@ LOCAL_LABEL(divby0):
 	JMP(lr)
 
 
-#if __ARM_ARCH_ISA_THUMB == 1
+#if defined(USE_THUMB_1)
 #define block(shift)                                                           \
 	lsls r2, r1, IMM shift;                                                      \
 	cmp r0, r2;                                                                  \
diff --git a/lib/builtins/arm/umodsi3.S b/lib/builtins/arm/umodsi3.S
index 672487e81..90f3e8575 100644
--- a/lib/builtins/arm/umodsi3.S
+++ b/lib/builtins/arm/umodsi3.S
@@ -16,7 +16,7 @@
 
 	.syntax unified
 	.text
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 	.thumb
 #endif
 
@@ -24,7 +24,7 @@
 @   Calculate and return the remainder of the (unsigned) division.
 
 	.p2align 2
-#if __ARM_ARCH_ISA_THUMB == 2
+#if defined(USE_THUMB_PROLOGUE)
 DEFINE_COMPILERRT_THUMB_FUNCTION(__umodsi3)
 #else
 DEFINE_COMPILERRT_FUNCTION(__umodsi3)
@@ -65,7 +65,7 @@ DEFINE_COMPILERRT_FUNCTION(__umodsi3)
 	clz	r3, r1
 	/* r0 >= r1 implies clz(r0) <= clz(r1), so ip <= r3. */
 	sub	r3, r3, ip
-#    if __ARM_ARCH_ISA_THUMB == 2
+#    if defined(USE_THUMB_2)
 	adr	ip, LOCAL_LABEL(div0block) + 1
 	sub	ip, ip, r3, lsl #1
 #    else
@@ -74,7 +74,7 @@ DEFINE_COMPILERRT_FUNCTION(__umodsi3)
 	sub	ip, ip, r3, lsl #3
 	bx	ip
 #  else
-#    if __ARM_ARCH_ISA_THUMB == 2
+#    if defined(USE_THUMB_2)
 #    error THUMB mode requires CLZ or UDIV
 #    endif
 	mov	r2, r0
diff --git a/lib/builtins/assembly.h b/lib/builtins/assembly.h
index 29d9f8844..af959b24b 100644
--- a/lib/builtins/assembly.h
+++ b/lib/builtins/assembly.h
@@ -92,20 +92,35 @@
   JMP(ip)
 #endif
 
-#if __ARM_ARCH_ISA_THUMB == 2
+/*
+ * Determine actual [ARM][THUMB[1][2]] ISA using compiler predefined macros:
+ * - for '-mthumb -march=armv6' compiler defines '__thumb__'
+ * - for '-mthumb -march=armv7' compiler defines '__thumb__' and '__thumb2__'
+ */
+#if defined(__thumb2__)
+#define USE_THUMB_2 1
+#elif defined(__thumb__)
+#define USE_THUMB_1 1
+#endif
+
+#if defined(USE_THUMB_1) && defined(USE_THUMB_2)
+#error "USE_THUMB_1 and USE_THUMB_2 can't be defined together."
+#endif
+
+#if defined(USE_THUMB_1) || defined(USE_THUMB_1)
+#define USE_THUMB_PROLOGUE 1
+#endif
+
+#if defined(USE_THUMB_2)
 #define IT(cond)  it cond
 #define ITT(cond) itt cond
+#define WIDE(op) op.w
 #else
 #define IT(cond)
 #define ITT(cond)
-#endif
-
-#if __ARM_ARCH_ISA_THUMB == 2
-#define WIDE(op) op.w
-#else
 #define WIDE(op) op
 #endif
-#endif
+#endif /* defined(__arm__) */
 
 #define GLUE2(a, b) a##b
 #define GLUE(a, b) GLUE2(a, b)