[SCEV] identical instructions don't compute equal values

Before this change `HasSameValue` would return true for distinct
`alloca` instructions if they happened to be allocating the same
type (`alloca` instructions are not specified as reading memory).  This
change adds an explicit whitelist of instruction types for which
"identical" instructions compute the same value.

Fixes PR24952.

llvm-svn: 248690

1 files changed, 27 insertions, 0 deletions

diff --git a/llvm/test/Transforms/IndVarSimplify/pr24952.ll b/llvm/test/Transforms/IndVarSimplify/pr24952.ll
new file mode 100644
index 00000000000..c430cae98f5
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/pr24952.ll
@@ -0,0 +1,27 @@
+; RUN: opt -indvars -S < %s | FileCheck %s
+
+declare void @use(i1)
+
+define void @f() {
+; CHECK-LABEL: @f(
+ entry:
+  %x = alloca i32
+  %y = alloca i32
+  br label %loop
+
+ loop:
+  %iv = phi i32 [ 0, %entry ], [ %iv.inc, %loop ]
+  %iv.inc = add i32 %iv, 1
+
+  %x.gep = getelementptr i32, i32* %x, i32 %iv
+  %eql = icmp eq i32* %x.gep, %y
+; CHECK-NOT: @use(i1 true)
+  call void @use(i1 %eql)
+
+  ; %be.cond deliberately 'false' -- we want want the trip count to be 0.
+  %be.cond = icmp ult i32 %iv, 0
+  br i1 %be.cond, label %loop, label %leave
+
+ leave:
+  ret void
+}