[LoopIdiom] Don't remove dead operands manually

Removing dead instructions requires remembering which operands have
already been removed.  RecursivelyDeleteTriviallyDeadInstructions has
this logic, don't partially reimplement it in LoopIdiomRecognize.

This fixes PR28196.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273132 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 26 insertions, 0 deletions

diff --git a/test/Transforms/LoopIdiom/pr28196.ll b/test/Transforms/LoopIdiom/pr28196.ll
new file mode 100644
index 00000000000..10f49fbcd09
--- /dev/null
+++ b/test/Transforms/LoopIdiom/pr28196.ll
@@ -0,0 +1,26 @@
+; RUN: opt -loop-idiom -S < %s | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @test1() {
+entry:
+  br label %for.body.preheader
+
+for.body.preheader:                               ; preds = %for.cond
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %for.body.preheader
+  %indvars.iv = phi i32 [ 0, %for.body.preheader ], [ %indvars.iv.next, %for.body ]
+  %add.ptr3 = getelementptr inbounds i32, i32* null, i32 %indvars.iv
+  %add.ptr4 = getelementptr inbounds i32, i32* %add.ptr3, i32 1
+  %0 = load i32, i32* %add.ptr4, align 4
+  store i32 %0, i32* %add.ptr3, align 4
+  %indvars.iv.next = add nsw i32 %indvars.iv, 1
+  %exitcond = icmp ne i32 %indvars.iv.next, 6
+  br i1 %exitcond, label %for.body, label %for.body.preheader
+}
+
+; CHECK-LABEL: define void @test1(
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* null, i8* inttoptr (i64 4 to i8*), i64 24, i32 4, i1 false)
+; CHECK-NOT: store