[PATCH] D74294: [InstCombine] Relax preconditions for ashr+and+icmp fold (PR44754)

[Nikita Popov via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
nikic marked an inline comment as done.
Closed by commit rG9adedd146d53: [InstCombine] Relax preconditions for ashr+and+icmp fold (PR44754) (authored by nikic).

Changed prior to commit:
  https://reviews.llvm.org/D74294?vs=243437&id=245176#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D74294/new/

https://reviews.llvm.org/D74294

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/icmp.ll


Index: llvm/test/Transforms/InstCombine/icmp.ll
===================================================================
--- llvm/test/Transforms/InstCombine/icmp.ll
+++ llvm/test/Transforms/InstCombine/icmp.ll
@@ -1864,9 +1864,8 @@
 
 define i1 @icmp_and_ashr_neg_and_legal(i8 %x) {
 ; CHECK-LABEL: @icmp_and_ashr_neg_and_legal(
-; CHECK-NEXT:    [[ASHR:%.*]] = ashr i8 [[X:%.*]], 4
-; CHECK-NEXT:    [[AND:%.*]] = and i8 [[ASHR]], -2
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[AND]], 1
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[X:%.*]], -32
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[TMP1]], 16
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %ashr = ashr i8 %x, 4
@@ -1891,9 +1890,8 @@
 
 define i1 @icmp_and_ashr_neg_cmp_slt_legal(i8 %x) {
 ; CHECK-LABEL: @icmp_and_ashr_neg_cmp_slt_legal(
-; CHECK-NEXT:    [[ASHR:%.*]] = ashr i8 [[X:%.*]], 4
-; CHECK-NEXT:    [[AND:%.*]] = and i8 [[ASHR]], -2
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[AND]], -4
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[X:%.*]], -32
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[TMP1]], -64
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %ashr = ashr i8 %x, 4
@@ -1918,9 +1916,8 @@
 
 define i1 @icmp_and_ashr_neg_cmp_eq_legal(i8 %x) {
 ; CHECK-LABEL: @icmp_and_ashr_neg_cmp_eq_legal(
-; CHECK-NEXT:    [[ASHR:%.*]] = ashr i8 [[X:%.*]], 4
-; CHECK-NEXT:    [[AND:%.*]] = and i8 [[ASHR]], -2
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[AND]], -4
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[X:%.*]], -32
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[TMP1]], -64
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %ashr = ashr i8 %x, 4
@@ -1931,10 +1928,7 @@
 
 define i1 @icmp_and_ashr_neg_cmp_eq_shiftout(i8 %x) {
 ; CHECK-LABEL: @icmp_and_ashr_neg_cmp_eq_shiftout(
-; CHECK-NEXT:    [[ASHR:%.*]] = ashr i8 [[X:%.*]], 4
-; CHECK-NEXT:    [[AND:%.*]] = and i8 [[ASHR]], -2
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[AND]], -68
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %ashr = ashr i8 %x, 4
   %and = and i8 %ashr, -2
@@ -1944,10 +1938,7 @@
 
 define i1 @icmp_and_ashr_neg_cmp_ne_shiftout(i8 %x) {
 ; CHECK-LABEL: @icmp_and_ashr_neg_cmp_ne_shiftout(
-; CHECK-NEXT:    [[ASHR:%.*]] = ashr i8 [[X:%.*]], 4
-; CHECK-NEXT:    [[AND:%.*]] = and i8 [[ASHR]], -2
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8 [[AND]], -68
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %ashr = ashr i8 %x, 4
   %and = and i8 %ashr, -2
Index: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1666,17 +1666,13 @@
       if (Cmp.isSigned() && (NewAndCst.isNegative() || NewCmpCst.isNegative()))
         return nullptr;
     } else {
-      // For an arithmetic shift right we can do the same, if we ensure
-      // the And doesn't use any bits being shifted in. Normally these would
-      // be turned into lshr by SimplifyDemandedBits, but not if there is an
-      // additional user.
+      // For an arithmetic shift, check that both constants don't use (in a
+      // signed sense) the top bits being shifted out.
       assert(ShiftOpcode == Instruction::AShr && "Unknown shift opcode");
       NewCmpCst = C1.shl(*C3);
       NewAndCst = C2.shl(*C3);
-      AnyCmpCstBitsShiftedOut = NewCmpCst.lshr(*C3) != C1;
-      if (NewAndCst.lshr(*C3) != C2)
-        return nullptr;
-      if (Cmp.isSigned() && (NewAndCst.isNegative() || NewCmpCst.isNegative()))
+      AnyCmpCstBitsShiftedOut = NewCmpCst.ashr(*C3) != C1;
+      if (NewAndCst.ashr(*C3) != C2)
         return nullptr;
     }
 


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