[ValueTracking] Calls to @llvm.assume always return

This change teaches llvm::isGuaranteedToTransferExecutionToSuccessor
that calls to @llvm.assume always terminate.  Most other relevant
intrinsics should be covered by the "CS.onlyReadsMemory() ||
CS.onlyAccessesArgMemory()" bit but we were missing @llvm.assumes
because we state that it clobbers memory.

Added an LICM test case, but this change is not specific to LICM.

llvm-svn: 272703

2 files changed, 20 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 7e09ec74bef..7109ff84b8e 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3478,7 +3478,8 @@ bool llvm::isGuaranteedToTransferExecutionToSuccessor(const Instruction *I) {
     // but it's consistent with other passes. See http://llvm.org/PR965 .
     // FIXME: This isn't aggressive enough; a call which only writes to a
     // global is guaranteed to return.
-    return CS.onlyReadsMemory() || CS.onlyAccessesArgMemory();
+    return CS.onlyReadsMemory() || CS.onlyAccessesArgMemory() ||
+           match(I, m_Intrinsic<Intrinsic::assume>());
   }
 
   // Other instructions return normally.
diff --git a/llvm/test/Transforms/LICM/assume.ll b/llvm/test/Transforms/LICM/assume.ll
index 9abf5578287..e426350ce73 100644
--- a/llvm/test/Transforms/LICM/assume.ll
+++ b/llvm/test/Transforms/LICM/assume.ll
@@ -1,6 +1,7 @@
 ; RUN: opt -licm -basicaa < %s -S | FileCheck %s
 
-define void @f(i1 %p) nounwind ssp {
+define void @f_0(i1 %p) nounwind ssp {
+; CHECK-LABEL: @f_0(
 entry:
   br label %for.body
 
@@ -31,4 +32,20 @@ for.end104:
   ret void
 }
 
+define void @f_1(i1 %cond, i32* %ptr) {
+; CHECK-LABEL: @f_1(
+; CHECK: %val = load i32, i32* %ptr
+; CHECK-NEXT:  br label %loop
+
+entry:
+  br label %loop
+
+loop:
+  %x = phi i32 [ 0, %entry ], [ %x.inc, %loop ]
+  call void @llvm.assume(i1 %cond)
+  %val = load i32, i32* %ptr
+  %x.inc = add i32 %x, %val
+  br label %loop
+}
+
 declare void @llvm.assume(i1)