[TargetLowering] optimizeSetCCToComparisonWithZero(): add extra sanity checks (PR43769)

We should do the fold only if both constants are plain,
non-opaque constants, at least that is the DAG.FoldConstantArithmetic()
requirement.
And if the constant we are comparing with is zero - we shouldn't be
trying to do this fold in the first place.

Fixes https://bugs.llvm.org/show_bug.cgi?id=43769

Author: LebedevRI

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -3052,6 +3052,10 @@ SDValue TargetLowering::optimizeSetCCToComparisonWithZero(
   assert((Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
          "Only for equality-comparisons.");
 
+  // The constant we are comparing with must be a non-zero, non-opaque constant.
+  if (N1C->isNullValue() || N1C->isOpaque())
+    return SDValue();
+
   // LHS should not be used elsewhere, to avoid creating an extra node.
   if (!N0.hasOneUse())
     return SDValue();
@@ -3072,9 +3076,9 @@ SDValue TargetLowering::optimizeSetCCToComparisonWithZero(
     break;
   }
 
-  // Second operand must be a constant.
+  // Second operand must be a non-opaque constant.
   ConstantSDNode *N01C = isConstOrConstSplat(N0.getOperand(1));
-  if (!N01C)
+  if (!N01C || N01C->isOpaque())
     return SDValue();
 
   // And let's be even more specific for now, it must be a zero constant.

llvm/test/CodeGen/X86/pr43769.ll

@@ -0,0 +1,54 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=i686-w64-windows-gnu %s -o - | FileCheck %s
+
+; Reduced from https://bugs.llvm.org/show_bug.cgi?id=43769
+
+define i32 @b(i32 %a, i32* %c, i32 %d) {
+; CHECK-LABEL: b:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    cmpl $0, {{[0-9]+}}(%esp)
+; CHECK-NEXT:    je LBB0_4
+; CHECK-NEXT:  # %bb.1: # %for.body.lr.ph
+; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; CHECK-NEXT:    movl %eax, %ecx
+; CHECK-NEXT:    sarl $31, %ecx
+; CHECK-NEXT:    addl $-2147483647, %eax # imm = 0x80000001
+; CHECK-NEXT:    adcl $0, %ecx
+; CHECK-NEXT:    jne LBB0_4
+; CHECK-NEXT:  # %bb.2: # %for.body.lr.ph.peel.newph
+; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; CHECK-NEXT:    movl $-2147483647, %edx # imm = 0x80000001
+; CHECK-NEXT:    movl %ecx, %eax
+; CHECK-NEXT:    sarl $31, %eax
+; CHECK-NEXT:    addl %ecx, %edx
+; CHECK-NEXT:    adcl $0, %eax
+; CHECK-NEXT:    .p2align 4, 0x90
+; CHECK-NEXT:  LBB0_3: # %for.body
+; CHECK-NEXT:    # =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    testl %eax, %eax
+; CHECK-NEXT:    je LBB0_3
+; CHECK-NEXT:  LBB0_4: # %for.end
+; CHECK-NEXT:    retl
+entry:
+  %tobool3 = icmp eq i32 %a, 0
+  br i1 %tobool3, label %for.end, label %for.body.lr.ph
+
+for.body.lr.ph:                                   ; preds = %entry
+  %0 = ptrtoint i32* %c to i32
+  %conv.peel = sext i32 %d to i64
+  %add.peel = add nsw i64 %conv.peel, 2147483649
+  %tobool1.peel = icmp ugt i64 %add.peel, 4294967295
+  br i1 %tobool1.peel, label %for.end, label %for.body.lr.ph.peel.newph
+
+for.body.lr.ph.peel.newph:                        ; preds = %for.body.lr.ph
+  %conv = sext i32 %0 to i64
+  %add = add nsw i64 %conv, 2147483649
+  %tobool1 = icmp ugt i64 %add, 4294967295
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %for.body.lr.ph.peel.newph
+  br i1 %tobool1, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body.lr.ph, %for.body, %entry
+  ret i32 undef
+}