If we have (select a, b, c), it is sometimes valid to simplify this to a
single select operand. However, doing so is only valid if the
computation doesn't inject poison into the computation.
It might be helpful to consider the following example:
(select (icmp ne %i, INT_MAX), (add nsw %i, 1), INT_MIN)
The select is equivalent to (add %i, 1) but not (add nsw %i, 1).
Self hosting on x86_64 revealed that this occurs very, very rarely so
bailing out is hopefully pretty reasonable.
llvm-svn: 239215
// If this is a binary operator, try to simplify it with the replaced op.
if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
+ // Consider:
+ // %cmp = icmp eq i32 %x, 2147483647
+ // %add = add nsw i32 %x, 1
+ // %sel = select i1 %cmp, i32 -2147483648, i32 %add
+ //
+ // We can't replace %sel with %add unless we strip away the flags.
+ if (isa<OverflowingBinaryOperator>(B))
+ if (B->hasNoSignedWrap() || B->hasNoUnsignedWrap())
+ return nullptr;
+ if (isa<PossiblyExactOperator>(B))
+ if (B->isExact())
+ return nullptr;
+
if (B->getOperand(0) == Op)
return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), DL, TLI);
if (B->getOperand(1) == Op)
%s1 = select i1 %c1, i32 %s0, i32 -1
ret i32 %s1
}
+
+
+define i32 @PR23757(i32 %x) {
+; CHECK-LABEL: @PR23757
+; CHECK: %[[cmp:.*]] = icmp eq i32 %x, 2147483647
+; CHECK-NEXT: %[[add:.*]] = add nsw i32 %x, 1
+; CHECK-NEXT: %[[sel:.*]] = select i1 %[[cmp]], i32 -2147483648, i32 %[[add]]
+; CHECK-NEXT: ret i32 %[[sel]]
+ %cmp = icmp eq i32 %x, 2147483647
+ %add = add nsw i32 %x, 1
+ %sel = select i1 %cmp, i32 -2147483648, i32 %add
+ ret i32 %sel
+}