[llvm] [SelectionDAG] Replace KnownZeros ugt check with MaskedValueIsZero check (PR #85573)

[via llvm-commits]

https://github.com/AtariDreams updated https://github.com/llvm/llvm-project/pull/85573

>From e377877edd1602a54fcf7f353eae43832530ef51 Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Sun, 17 Mar 2024 14:04:52 -0400
Subject: [PATCH 1/2] [SelecttionDAG] Precommit tests (NFC)

---
 llvm/test/CodeGen/X86/dagcombine-shifts.ll | 44 ++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/llvm/test/CodeGen/X86/dagcombine-shifts.ll b/llvm/test/CodeGen/X86/dagcombine-shifts.ll
index 42b325dd4c229e..0795e99669c6e0 100644
--- a/llvm/test/CodeGen/X86/dagcombine-shifts.ll
+++ b/llvm/test/CodeGen/X86/dagcombine-shifts.ll
@@ -322,5 +322,49 @@ define void @g(i32 %a) nounwind {
   ret void
 }
 
+define i32 @shift_zext_shl(i8 zeroext %x) {
+; X86-LABEL: shift_zext_shl:
+; X86:       # %bb.0:
+; X86-NEXT:    movzbl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    andb $64, %al
+; X86-NEXT:    movzbl %al, %eax
+; X86-NEXT:    shll $9, %eax
+; X86-NEXT:    movzwl %ax, %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: shift_zext_shl:
+; X64:       # %bb.0:
+; X64-NEXT:    andb $64, %dil
+; X64-NEXT:    movzbl %dil, %eax
+; X64-NEXT:    shll $9, %eax
+; X64-NEXT:    movzwl %ax, %eax
+; X64-NEXT:    retq
+  %1 = and i8 %x, 64
+  %2 = zext i8 %1 to i16
+  %3 = shl i16 %2, 9
+  %4 = zext i16 %3 to i32
+  ret i32 %4
+}
+
+define i32 @shift_zext_shl2(i8 zeroext %x) {
+; X86-LABEL: shift_zext_shl2:
+; X86:       # %bb.0:
+; X86-NEXT:    movzbl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    andl $64, %eax
+; X86-NEXT:    shll $9, %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: shift_zext_shl2:
+; X64:       # %bb.0:
+; X64-NEXT:    movl %edi, %eax
+; X64-NEXT:    andl $64, %eax
+; X64-NEXT:    shll $9, %eax
+; X64-NEXT:    retq
+  %1 = and i8 %x, 64
+  %2 = zext i8 %1 to i32
+  %3 = shl i32 %2, 9
+  ret i32 %3
+}
+
 declare dso_local void @f(i64)
 

>From 46c20239afb5f140cfb702702a388a9fecb44408 Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Sun, 17 Mar 2024 12:51:41 -0400
Subject: [PATCH 2/2] [SelectionDAG] Replace KnownZeros ugt check with
 MaskedValueIsZero check

Add ones for every high bit that will cleared.

We can remove the ugt check because if the masked value is not zero, then ugt will always be true anyway.
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 13 +++++++++----
 llvm/test/CodeGen/X86/dagcombine-shifts.ll    |  9 +++------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 5eb53d57c9c2bf..9181f90f602792 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -13802,11 +13802,16 @@ SDValue DAGCombiner::visitZERO_EXTEND(SDNode *N) {
         if (N0.getOpcode() == ISD::SHL) {
           // If the original shl may be shifting out bits, do not perform this
           // transformation.
-          // TODO: Add MaskedValueIsZero check.
-          unsigned KnownZeroBits = ShVal.getValueSizeInBits() -
-                                   ShVal.getOperand(0).getValueSizeInBits();
-          if (ShAmtC->getAPIntValue().ugt(KnownZeroBits))
+
+          // Create a mask that has ones for the bits being shifted out.
+          llvm::APInt ShiftOutMask = llvm::APInt::getHighBitsSet(
+              ShVal.getValueSizeInBits(),
+              ShAmtC->getAPIntValue().getZExtValue());
+
+          // Check if the bits being shifted out are known to be zero.
+          if (!DAG.MaskedValueIsZero(ShVal, ShiftOutMask)) {
             return SDValue();
+          }
         }
 
         // Ensure that the shift amount is wide enough for the shifted value.
diff --git a/llvm/test/CodeGen/X86/dagcombine-shifts.ll b/llvm/test/CodeGen/X86/dagcombine-shifts.ll
index 0795e99669c6e0..2322277aef2e32 100644
--- a/llvm/test/CodeGen/X86/dagcombine-shifts.ll
+++ b/llvm/test/CodeGen/X86/dagcombine-shifts.ll
@@ -326,18 +326,15 @@ define i32 @shift_zext_shl(i8 zeroext %x) {
 ; X86-LABEL: shift_zext_shl:
 ; X86:       # %bb.0:
 ; X86-NEXT:    movzbl {{[0-9]+}}(%esp), %eax
-; X86-NEXT:    andb $64, %al
-; X86-NEXT:    movzbl %al, %eax
+; X86-NEXT:    andl $64, %eax
 ; X86-NEXT:    shll $9, %eax
-; X86-NEXT:    movzwl %ax, %eax
 ; X86-NEXT:    retl
 ;
 ; X64-LABEL: shift_zext_shl:
 ; X64:       # %bb.0:
-; X64-NEXT:    andb $64, %dil
-; X64-NEXT:    movzbl %dil, %eax
+; X64-NEXT:    movl %edi, %eax
+; X64-NEXT:    andl $64, %eax
 ; X64-NEXT:    shll $9, %eax
-; X64-NEXT:    movzwl %ax, %eax
 ; X64-NEXT:    retq
   %1 = and i8 %x, 64
   %2 = zext i8 %1 to i16