[X86] isGuaranteedNotToBeUndefOrPoison - add simple target shuffles with known test coverage

[RKSimon]

Add a number of simple target shuffles (fixed shuffle mask or simple immediate control) to isGuaranteedNotToBeUndefOrPoison/canCreateUndefOrPoisonForTargetNode that have known test coverage and obviously don't introduce undef/poison.

These were found by adding an assert for unhandled target shuffles and running over CodeGen/X86 - providing explicit test coverage is incredibly difficult as ISD::VECTOR_SHUFFLE nodes will typically handle freeze nodes before we lower to these target shuffle nodes.

[llvmbot]

@llvm/pr-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

Changes

Add a number of simple target shuffles (fixed shuffle mask or simple immediate control) to isGuaranteedNotToBeUndefOrPoison/canCreateUndefOrPoisonForTargetNode that have known test coverage and obviously don't introduce undef/poison.

These were found by adding an assert for unhandled target shuffles and running over CodeGen/X86 - providing explicit test coverage is incredibly difficult as ISD::VECTOR_SHUFFLE nodes will typically handle freeze nodes before we lower to these target shuffle nodes.

---

Full diff: https://github.com/llvm/llvm-project/pull/161553.diff

1 Files Affected:

• (modified) llvm/lib/Target/X86/X86ISelLowering.cpp (+21)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 34854e4d8b6c0..4f8b371651e7e 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -45187,11 +45187,16 @@ bool X86TargetLowering::isGuaranteedNotToBeUndefOrPoisonForTargetNode(
   case X86ISD::INSERTPS:
   case X86ISD::BLENDI:
   case X86ISD::PSHUFB:
+  case X86ISD::VZEXT_MOVL:
   case X86ISD::PSHUFD:
+  case X86ISD::PSHUFHW:
+  case X86ISD::PSHUFLW:
+  case X86ISD::SHUFP:
   case X86ISD::UNPCKL:
   case X86ISD::UNPCKH:
   case X86ISD::VPERMILPV:
   case X86ISD::VPERMILPI:
+  case X86ISD::VPERMI:
   case X86ISD::VPERMV:
   case X86ISD::VPERMV3: {
     SmallVector<int, 8> Mask;
@@ -45217,6 +45222,16 @@ bool X86TargetLowering::isGuaranteedNotToBeUndefOrPoisonForTargetNode(
     }
     break;
   }
+  case X86ISD::VBROADCAST: {
+    SDValue Src = Op.getOperand(0);
+    MVT SrcVT = Src.getSimpleValueType();
+    if (SrcVT.isVector()) {
+      APInt DemandedSrc = APInt::getOneBitSet(SrcVT.getVectorNumElements(), 0);
+      return DAG.isGuaranteedNotToBeUndefOrPoison(Src, DemandedSrc, PoisonOnly,
+                                                  Depth + 1);
+    }
+    return DAG.isGuaranteedNotToBeUndefOrPoison(Src, PoisonOnly, Depth + 1);
+  }
   }
   return TargetLowering::isGuaranteedNotToBeUndefOrPoisonForTargetNode(
       Op, DemandedElts, DAG, PoisonOnly, Depth);
@@ -45261,13 +45276,19 @@ bool X86TargetLowering::canCreateUndefOrPoisonForTargetNode(
   // SSE target shuffles.
   case X86ISD::INSERTPS:
   case X86ISD::PSHUFB:
+  case X86ISD::VZEXT_MOVL:
   case X86ISD::PSHUFD:
+  case X86ISD::PSHUFHW:
+  case X86ISD::PSHUFLW:
+  case X86ISD::SHUFP:
   case X86ISD::UNPCKL:
   case X86ISD::UNPCKH:
   case X86ISD::VPERMILPV:
   case X86ISD::VPERMILPI:
+  case X86ISD::VPERMI:
   case X86ISD::VPERMV:
   case X86ISD::VPERMV3:
+  case X86ISD::VBROADCAST:
     return false;
   // SSE comparisons handle all icmp/fcmp cases.
   // TODO: Add CMPM/MM with test coverage.

[bjope]

Need to say that I'm not that familiar with the details for all these X86ISD nodes. The patch looks good to me, but maybe you want a second opinion from someone more experienced with X86.