[PATCH] D88072: [X86] Improve demanded bits for X86ISD::BEXTR.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: spatel, RKSimon.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.
craig.topper requested review of this revision.

If the control is constant we can figure out exactly which bits
of the input are demanded.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D88072

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/tbm-intrinsics.ll


Index: llvm/test/CodeGen/X86/tbm-intrinsics.ll
===================================================================
--- llvm/test/CodeGen/X86/tbm-intrinsics.ll
+++ llvm/test/CodeGen/X86/tbm-intrinsics.ll
@@ -61,3 +61,18 @@
   %2 = select i1 %1, i32 %b, i32 %0
   ret i32 %2
 }
+
+define i32 @test_x86_tbm_bextri_demandedbits(i32 %x) nounwind readonly {
+; X86-LABEL: test_x86_tbm_bextri_demandedbits:
+; X86:       # %bb.0:
+; X86-NEXT:    bextrl $3841, {{[0-9]+}}(%esp), %eax # imm = 0xF01
+; X86-NEXT:    retl
+;
+; X64-LABEL: test_x86_tbm_bextri_demandedbits:
+; X64:       # %bb.0:
+; X64-NEXT:    bextrl $3841, %edi, %eax # imm = 0xF01
+; X64-NEXT:    retq
+  %a = or i32 %x, 4294901761
+  %b = tail call i32 @llvm.x86.tbm.bextri.u32(i32 %a, i32 3841)
+  ret i32 %b
+}
Index: llvm/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -38332,6 +38332,25 @@
             Op, TLO.DAG.getNode(X86ISD::BEXTR, DL, VT, Op0,
                                 TLO.DAG.getConstant(MaskedVal1, DL, VT)));
       }
+
+      unsigned Shift = Cst1->getAPIntValue().extractBitsAsZExtValue(8, 0);
+      unsigned Length = Cst1->getAPIntValue().extractBitsAsZExtValue(8, 8);
+
+      // If the length is 0, the result is 0.
+      if (Length == 0) {
+        Known.setAllZero();
+        return false;
+      }
+
+      if ((Shift + Length) <= BitWidth) {
+        APInt DemandedMask = APInt::getBitsSet(BitWidth, Shift, Shift + Length);
+        if (SimplifyDemandedBits(Op0, DemandedMask, Known, TLO, Depth + 1))
+          return true;
+
+        Known = Known.extractBits(Length, Shift);
+        Known = Known.zextOrTrunc(BitWidth);
+        return false;
+      }
     }
 
     KnownBits Known1;


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