[PATCH] D116469: [AMDGPU] Correct the known bits calculation for MUL_I24.

[Craig Topper via Phabricator via llvm-commits]

craig.topper updated this revision to Diff 396989.
craig.topper added a comment.

Address Simon's comments.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D116469/new/

https://reviews.llvm.org/D116469

Files:
  llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp


Index: llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
+++ llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
@@ -4626,11 +4626,12 @@
     RHSKnown = RHSKnown.trunc(24);
 
     if (Opc == AMDGPUISD::MUL_I24) {
-      unsigned LHSValBits = 24 - LHSKnown.countMinSignBits();
-      unsigned RHSValBits = 24 - RHSKnown.countMinSignBits();
-      unsigned MaxValBits = std::min(LHSValBits + RHSValBits, 32u);
-      if (MaxValBits >= 32)
+      unsigned LHSValBits = LHSKnown.countMaxSignedBits();
+      unsigned RHSValBits = RHSKnown.countMaxSignedBits();
+      unsigned MaxValBits = LHSValBits + RHSValBits;
+      if (MaxValBits > 32)
         break;
+      unsigned SignBits = 32 - MaxValBits + 1;
       bool LHSNegative = LHSKnown.isNegative();
       bool LHSNonNegative = LHSKnown.isNonNegative();
       bool LHSPositive = LHSKnown.isStrictlyPositive();
@@ -4639,16 +4640,16 @@
       bool RHSPositive = RHSKnown.isStrictlyPositive();
 
       if ((LHSNonNegative && RHSNonNegative) || (LHSNegative && RHSNegative))
-        Known.Zero.setHighBits(32 - MaxValBits);
+        Known.Zero.setHighBits(SignBits);
       else if ((LHSNegative && RHSPositive) || (LHSPositive && RHSNegative))
-        Known.One.setHighBits(32 - MaxValBits);
+        Known.One.setHighBits(SignBits);
     } else {
-      unsigned LHSValBits = 24 - LHSKnown.countMinLeadingZeros();
-      unsigned RHSValBits = 24 - RHSKnown.countMinLeadingZeros();
-      unsigned MaxValBits = std::min(LHSValBits + RHSValBits, 32u);
+      unsigned LHSValBits = LHSKnown.countMaxActiveBits();
+      unsigned RHSValBits = RHSKnown.countMaxActiveBits();
+      unsigned MaxValBits = LHSValBits + RHSValBits;
       if (MaxValBits >= 32)
         break;
-      Known.Zero.setHighBits(32 - MaxValBits);
+      Known.Zero.setBitsFrom(MaxValBits);
     }
     break;
   }


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