[DAGCombine] Fix for PR35761

[samparker]

Summary

I had falsely assumed that constant operands would be operand(1) of the bin ops that may need their constant operand to be masked.

Bugzilla: https://bugs.llvm.org/show_bug.cgi?id=35761

[RKSimon]

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

3924 ↗

(On Diff #128420)

It might be clearer if you just do something like:

SDValue Op0 = LogicN->getOperand(0);
SDValue Op1 = LogicN->getOperand(1);

if (isa<ConstantSDNode>(Op0))
  std::swap(Op0, Op1);

SDValue And = DAG.getNode(ISD::AND, SDLoc(Op1), Op1.getValueType(), Op1, MaskOp);
DAG.UpdateNodeOperands(LogicN, Op0, And);

test/CodeGen/X86/pr35761.ll

66 ↗

(On Diff #128420)

Please can you try to reduce this further

[samparker]

Thanks for the suggestion Simon, I've now implemented it and simplified the test.

[RKSimon]

LGTM - thanks

llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

if (FixupNode) {
                                 SDValue(FixupNode, 0), MaskOp);
       DAG.ReplaceAllUsesOfValueWith(SDValue(FixupNode, 0), And);
       DAG.UpdateNodeOperands(And.getNode(), SDValue(FixupNode, 0),
                              MaskOp);
     }
 
     // Narrow any constants that need it.
     for (auto *LogicN : NodesWithConsts) {
-      auto *C = cast<ConstantSDNode>(LogicN->getOperand(1));
-      SDValue And = DAG.getNode(ISD::AND, SDLoc(C), C->getValueType(0),
-                                SDValue(C, 0), MaskOp);
-      DAG.UpdateNodeOperands(LogicN, LogicN->getOperand(0), And);
+      SDValue Op0 = LogicN->getOperand(0);
+      SDValue Op1 = LogicN->getOperand(1);
+
+      if (isa<ConstantSDNode>(Op0))
+          std::swap(Op0, Op1);
+
+      SDValue And = DAG.getNode(ISD::AND, SDLoc(Op1), Op1.getValueType(),
+                                Op1, MaskOp);
+
+      DAG.UpdateNodeOperands(LogicN, Op0, And);
     }
 
     // Create narrow loads.
     for (auto *Load : Loads) {
       DEBUG(dbgs() << "Propagate AND back to: "; Load->dump());
       SDValue And = DAG.getNode(ISD::AND, SDLoc(Load), Load->getValueType(0),
                                 SDValue(Load, 0), MaskOp);
       DAG.ReplaceAllUsesOfValueWith(SDValue(Load, 0), And);

llvm/trunk/test/CodeGen/X86/pr35761.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=x86_64-unknown-linux %s -o - | FileCheck %s
+
+@x = global i8 0, align 1
+@y = global i32 0, align 4
+@z = global i24 0, align 4
+
+define void @PR35761(i32 %call) {
+; CHECK-LABEL: PR35761:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    movzbl {{.*}}(%rip), %eax
+; CHECK-NEXT:    andl $1, %eax
+; CHECK-NEXT:    movzbl {{.*}}(%rip), %ecx
+; CHECK-NEXT:    xorl $255, %ecx
+; CHECK-NEXT:    orl %eax, %ecx
+; CHECK-NEXT:    movw %cx, {{.*}}(%rip)
+; CHECK-NEXT:    movb $0, z+{{.*}}(%rip)
+; CHECK-NEXT:    retq
+entry:
+  %0 = load i8, i8* @x, align 1
+  %tobool = trunc i8 %0 to i1
+  %conv = zext i1 %tobool to i32
+  %or = or i32 32767, %call
+  %neg = xor i32 %or, -1
+  %neg1 = xor i32 %neg, -1
+  %1 = load i32, i32* @y, align 4
+  %xor = xor i32 %neg1, %1
+  %or2 = or i32 %conv, %xor
+  %conv3 = trunc i32 %or2 to i8
+  %bf.load = load i24, i24* @z, align 4
+  %2 = zext i8 %conv3 to i24
+  %bf.value = and i24 %2, 4194303
+  store i24 %bf.value, i24* @z, align 2
+  ret void
+}
+