[llvm] e43a085 - [X86] X86::isConstantSplat - enable partial undef bit handling by default.

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-03-16T12:56:24Z
New Revision: e43a0857818740184915043cbe2ceb2d3849fcae

URL: https://github.com/llvm/llvm-project/commit/e43a0857818740184915043cbe2ceb2d3849fcae
DIFF: https://github.com/llvm/llvm-project/commit/e43a0857818740184915043cbe2ceb2d3849fcae.diff

LOG: [X86] X86::isConstantSplat - enable partial undef bit handling by default.

We currently only ever use this for lowering constant uniform values (shift/rotate by immediate) so we can safely enable it by default (it treats the undef bits as zero when extracting constants).

This is necessary for an upcoming patch that will use SimplifyDemandedBits more aggressively on funnel shift amounts and causes regressions in vXi64 constant without it.

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelLowering.cpp
    llvm/lib/Target/X86/X86ISelLowering.h

Removed: 
    


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diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index e25dc0242878..339e3c37ee25 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -6528,11 +6528,12 @@ static bool getTargetConstantBitsFromNode(SDValue Op, unsigned EltSizeInBits,
 
 namespace llvm {
 namespace X86 {
-bool isConstantSplat(SDValue Op, APInt &SplatVal) {
+bool isConstantSplat(SDValue Op, APInt &SplatVal, bool AllowPartialUndefs) {
   APInt UndefElts;
   SmallVector<APInt, 16> EltBits;
   if (getTargetConstantBitsFromNode(Op, Op.getScalarValueSizeInBits(),
-                                    UndefElts, EltBits, true, false)) {
+                                    UndefElts, EltBits, true,
+                                    AllowPartialUndefs)) {
     int SplatIndex = -1;
     for (int i = 0, e = EltBits.size(); i != e; ++i) {
       if (UndefElts[i])

diff  --git a/llvm/lib/Target/X86/X86ISelLowering.h b/llvm/lib/Target/X86/X86ISelLowering.h
index 0da22acc99de..825ddedad176 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.h
+++ b/llvm/lib/Target/X86/X86ISelLowering.h
@@ -722,7 +722,10 @@ namespace llvm {
 
     /// If Op is a constant whose elements are all the same constant or
     /// undefined, return true and return the constant value in \p SplatVal.
-    bool isConstantSplat(SDValue Op, APInt &SplatVal);
+    /// If we have undef bits that don't cover an entire element, we treat these
+    /// as zero if AllowPartialUndefs is set, else we fail and return false.
+    bool isConstantSplat(SDValue Op, APInt &SplatVal,
+                         bool AllowPartialUndefs = true);
   } // end namespace X86
 
   //===--------------------------------------------------------------------===//