[llvm] a5be86f - [InstSimplify] Protect against more poison in SimplifyWithOpReplaced (PR47322)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2020-08-29T21:59:39+02:00
New Revision: a5be86fde5de2c253aa19704bf4e4854f1936f8c

URL: https://github.com/llvm/llvm-project/commit/a5be86fde5de2c253aa19704bf4e4854f1936f8c
DIFF: https://github.com/llvm/llvm-project/commit/a5be86fde5de2c253aa19704bf4e4854f1936f8c.diff

LOG: [InstSimplify] Protect against more poison in SimplifyWithOpReplaced (PR47322)

Replace the check for poison-producing instructions in
SimplifyWithOpReplaced() with the generic helper canCreatePoison()
that properly handles poisonous shifts and thus avoids the problem
from PR47322.

This additionally fixes a bug in IIQ.UseInstrInfo=false mode, which
previously could have caused this code to ignore poison flags.
Setting UseInstrInfo=false should reduce the possible optimizations,
not increase them.

This is not a full solution to the problem, as poison could be
introduced more indirectly. This is just a minimal, easy to backport
fix.

Differential Revision: https://reviews.llvm.org/D86834

Added: 
    

Modified: 
    llvm/lib/Analysis/InstructionSimplify.cpp
    llvm/test/Transforms/InstSimplify/select.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index ae4f2804f7af..fdb9a0b6fcf7 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3796,10 +3796,7 @@ static const Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
     // TODO: This is an unusual limitation because better analysis results in
     //       worse simplification. InstCombine can do this fold more generally
     //       by dropping the flags. Remove this fold to save compile-time?
-    if (isa<OverflowingBinaryOperator>(B))
-      if (Q.IIQ.hasNoSignedWrap(B) || Q.IIQ.hasNoUnsignedWrap(B))
-        return nullptr;
-    if (isa<PossiblyExactOperator>(B) && Q.IIQ.isExact(B))
+    if (canCreatePoison(cast<Operator>(I)))
       return nullptr;
 
     if (MaxRecurse) {

diff  --git a/llvm/test/Transforms/InstSimplify/select.ll b/llvm/test/Transforms/InstSimplify/select.ll
index c4d84492d02e..2dcd29753788 100644
--- a/llvm/test/Transforms/InstSimplify/select.ll
+++ b/llvm/test/Transforms/InstSimplify/select.ll
@@ -941,3 +941,19 @@ define i1 @expand_binop_undef(i32 %x, i32 %y) {
   %spec.select  = and i1 %spec.select39, %spec.select40
   ret i1 %spec.select
 }
+
+define i32 @pr47322_more_poisonous_replacement(i32 %arg) {
+; CHECK-LABEL: @pr47322_more_poisonous_replacement(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[ARG:%.*]], 0
+; CHECK-NEXT:    [[TRAILING:%.*]] = call i32 @llvm.cttz.i32(i32 [[ARG]], i1 immarg true)
+; CHECK-NEXT:    [[SHIFTED:%.*]] = lshr i32 [[ARG]], [[TRAILING]]
+; CHECK-NEXT:    [[R1_SROA_0_1:%.*]] = select i1 [[CMP]], i32 0, i32 [[SHIFTED]]
+; CHECK-NEXT:    ret i32 [[R1_SROA_0_1]]
+;
+  %cmp = icmp eq i32 %arg, 0
+  %trailing = call i32 @llvm.cttz.i32(i32 %arg, i1 immarg true)
+  %shifted = lshr i32 %arg, %trailing
+  %r1.sroa.0.1 = select i1 %cmp, i32 0, i32 %shifted
+  ret i32 %r1.sroa.0.1
+}
+declare i32 @llvm.cttz.i32(i32, i1 immarg)