[llvm] r355292 - [ValueTracking] do not try to peek through bitcasts in computeKnownBitsFromAssume()

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Sun Mar  3 10:59:33 2019
New Revision: 355292

URL: http://llvm.org/viewvc/llvm-project?rev=355292&view=rev
Log:
[ValueTracking] do not try to peek through bitcasts in computeKnownBitsFromAssume()

There are no tests for this case, and I'm not sure how it could ever work,
so I'm just removing this option from the matcher. This should fix PR40940:
https://bugs.llvm.org/show_bug.cgi?id=40940

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

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=355292&r1=355291&r2=355292&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Sun Mar  3 10:59:33 2019
@@ -617,9 +617,7 @@ static void computeKnownBitsFromAssume(c
       continue;
 
     Value *A, *B;
-    auto m_V = m_CombineOr(m_Specific(V),
-                           m_CombineOr(m_PtrToInt(m_Specific(V)),
-                           m_BitCast(m_Specific(V))));
+    auto m_V = m_CombineOr(m_Specific(V), m_PtrToInt(m_Specific(V)));
 
     CmpInst::Predicate Pred;
     uint64_t C;

Modified: llvm/trunk/test/Transforms/InstCombine/assume.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/assume.ll?rev=355292&r1=355291&r2=355292&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/assume.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/assume.ll Sun Mar  3 10:59:33 2019
@@ -320,6 +320,24 @@ define void @debug_interference(i8 %x) {
   ret void
 }
 
+; This would crash.
+; Does it ever make sense to peek through a bitcast of the icmp operand?
+
+define i32 @PR40940(<4 x i8> %x) {
+; CHECK-LABEL: @PR40940(
+; CHECK-NEXT:    [[SHUF:%.*]] = shufflevector <4 x i8> [[X:%.*]], <4 x i8> undef, <4 x i32> <i32 1, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    [[T2:%.*]] = bitcast <4 x i8> [[SHUF]] to i32
+; CHECK-NEXT:    [[T3:%.*]] = icmp ult i32 [[T2]], 65536
+; CHECK-NEXT:    call void @llvm.assume(i1 [[T3]])
+; CHECK-NEXT:    ret i32 [[T2]]
+;
+  %shuf = shufflevector <4 x i8> %x, <4 x i8> undef, <4 x i32> <i32 1, i32 1, i32 2, i32 3>
+  %t2 = bitcast <4 x i8> %shuf to i32
+  %t3 = icmp ult i32 %t2, 65536
+  call void @llvm.assume(i1 %t3)
+  ret i32 %t2
+}
+
 declare void @llvm.dbg.value(metadata, metadata, metadata)
 
 !llvm.dbg.cu = !{!0}