[PATCH] D145811: [SystemZ] Don't reuse a sub that can overflow during isel.

[Jonas Paulsson via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGf8803919ad5c: [SystemZ] Clear NW flags on an ISD::SUB when reused as comparison. (authored by jonpa).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D145811/new/

https://reviews.llvm.org/D145811

Files:
  llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
  llvm/test/CodeGen/SystemZ/int-cmp-62.ll


Index: llvm/test/CodeGen/SystemZ/int-cmp-62.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/SystemZ/int-cmp-62.ll
@@ -0,0 +1,39 @@
+; RUN: llc < %s -mtriple=s390x-linux-gnu -mcpu=z15 | FileCheck %s
+;
+; Test that a CC result of a sub that can overflow is tested with the right predicate.
+
+define i32 @fun0(i32 %a, i32 %b, ptr %dest) {
+; CHECK-LABEL: fun0
+; CHECK: s %r2, 0(%r4)
+; CHECK: bner %r14
+entry:
+  %cur = load i32, ptr %dest
+  %res = sub nsw i32 %a, %cur
+  %cmp = icmp ne i32 %a, %cur
+  br i1 %cmp, label %exit, label %store
+
+store:
+  store i32 %b, ptr %dest
+  br label %exit
+
+exit:
+  ret i32 %res
+}
+
+define i32 @fun1(i32 %a, i32 %b, ptr %dest) {
+; CHECK-LABEL: fun1
+; CHECK: s %r2, 0(%r4)
+; CHECK: bner %r14
+entry:
+  %cur = load i32, ptr %dest
+  %res = sub nuw i32 %a, %cur
+  %cmp = icmp ne i32 %a, %cur
+  br i1 %cmp, label %exit, label %store
+
+store:
+  store i32 %b, ptr %dest
+  br label %exit
+
+exit:
+  ret i32 %res
+}
Index: llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
===================================================================
--- llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -2423,6 +2423,12 @@
       if (N->getOpcode() == ISD::SUB &&
           ((N->getOperand(0) == C.Op0 && N->getOperand(1) == C.Op1) ||
            (N->getOperand(0) == C.Op1 && N->getOperand(1) == C.Op0))) {
+        // Disable the nsw and nuw flags: the backend needs to handle
+        // overflow as well during comparison elimination.
+        SDNodeFlags Flags = N->getFlags();
+        Flags.setNoSignedWrap(false);
+        Flags.setNoUnsignedWrap(false);
+        N->setFlags(Flags);
         C.Op0 = SDValue(N, 0);
         C.Op1 = DAG.getConstant(0, DL, N->getValueType(0));
         return;


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