[llvm] r368723 - [ValueTracking] Improve reverse assumption inference

[Nikita Popov via llvm-commits]

Author: nikic
Date: Tue Aug 13 10:15:42 2019
New Revision: 368723

URL: http://llvm.org/viewvc/llvm-project?rev=368723&view=rev
Log:
[ValueTracking] Improve reverse assumption inference

Use isGuaranteedToTransferExecutionToSuccessor() instead of
isSafeToSpeculativelyExecute() when seeing whether we can propagate
the information in an assume backwards in isValidAssumeForContext().
The latter is more general - it also allows arbitrary loads/stores -
and is also the condition we want: if our assume is guaranteed to
execute, its condition not holding would be UB.

Original patch by arielb1.

Differential Revision: https://reviews.llvm.org/D37215

Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp
    llvm/trunk/test/Transforms/InstCombine/assume_inevitable.ll

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=368723&r1=368722&r2=368723&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Tue Aug 13 10:15:42 2019
@@ -558,12 +558,18 @@ bool llvm::isValidAssumeForContext(const
         return true;
   }
 
+  // Don't let an assume affect itself - this would cause the problems
+  // `isEphemeralValueOf` is trying to prevent, and it would also make
+  // the loop below go out of bounds.
+  if (Inv == CxtI)
+    return false;
+
   // The context comes first, but they're both in the same block. Make sure
   // there is nothing in between that might interrupt the control flow.
   for (BasicBlock::const_iterator I =
          std::next(BasicBlock::const_iterator(CxtI)), IE(Inv);
        I != IE; ++I)
-    if (!isSafeToSpeculativelyExecute(&*I) && !isAssumeLikeIntrinsic(&*I))
+    if (!isGuaranteedToTransferExecutionToSuccessor(&*I))
       return false;
 
   return !isEphemeralValueOf(Inv, CxtI);

Modified: llvm/trunk/test/Transforms/InstCombine/assume_inevitable.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/assume_inevitable.ll?rev=368723&r1=368722&r2=368723&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/assume_inevitable.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/assume_inevitable.ll Tue Aug 13 10:15:42 2019
@@ -8,10 +8,10 @@ define i32 @assume_inevitable(i32* %a, i
 ; CHECK-LABEL: @assume_inevitable(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[M:%.*]] = alloca i64, align 8
-; CHECK-NEXT:    [[TMP0:%.*]] = load i32, i32* [[A:%.*]], align 4
+; CHECK-NEXT:    [[TMP0:%.*]] = load i32, i32* [[A:%.*]], align 32
 ; CHECK-NEXT:    [[LOADRES:%.*]] = load i32, i32* [[B:%.*]], align 4
 ; CHECK-NEXT:    [[LOADRES2:%.*]] = call i32 @llvm.annotation.i32(i32 [[LOADRES]], i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str, i64 0, i64 0), i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str1, i64 0, i64 0), i32 2)
-; CHECK-NEXT:    store i32 [[LOADRES2]], i32* [[A]], align 4
+; CHECK-NEXT:    store i32 [[LOADRES2]], i32* [[A]], align 32
 ; CHECK-NEXT:    [[DUMMY_EQ:%.*]] = icmp ugt i32 [[LOADRES]], 42
 ; CHECK-NEXT:    tail call void @llvm.assume(i1 [[DUMMY_EQ]])
 ; CHECK-NEXT:    [[M_I8:%.*]] = bitcast i64* [[M]] to i8*