[PATCH] D25913: [InstCombine] Fold nuw left-shifts in `ugt`/`ule` comparisons.

[bryant via llvm-commits]

bryant updated this revision to Diff 75631.
bryant added a comment.

- Handle the vector case properly.
- Remove redundant tests.
- Test vector and non-zero cases.


Repository:
  rL LLVM

https://reviews.llvm.org/D25913

Files:
  lib/Transforms/InstCombine/InstCombineCompares.cpp
  test/Transforms/InstCombine/icmp-shl-zext-simplify.ll


Index: test/Transforms/InstCombine/icmp-shl-zext-simplify.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/icmp-shl-zext-simplify.ll
@@ -0,0 +1,44 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt %s -instcombine -S | FileCheck %s
+
+define i1 @icmp_ugt_32(i64) {
+; CHECK-LABEL: @icmp_ugt_32(
+; CHECK-NEXT:    [[D:%.*]] = icmp ne i64 %0, 0
+; CHECK-NEXT:    ret i1 [[D]]
+;
+  %c = shl nuw i64 %0, 32
+  %d = icmp ugt i64 %c, 4294967295
+  ret i1 %d
+}
+
+define i1 @icmp_ule_64(i128) {
+; CHECK-LABEL: @icmp_ule_64(
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc i128 %0 to i64
+; CHECK-NEXT:    [[D:%.*]] = icmp eq i64 [[TMP2]], 0
+; CHECK-NEXT:    ret i1 [[D]]
+;
+  %c = shl nuw i128 %0, 64
+  %d = icmp ule i128 %c, 18446744073709551615
+  ret i1 %d
+}
+
+define i1 @icmp_ugt_16(i64) {
+; CHECK-LABEL: @icmp_ugt_16(
+; CHECK-NEXT:    [[D:%.*]] = icmp ugt i64 %0, 15
+; CHECK-NEXT:    ret i1 [[D]]
+;
+  %c = shl nuw i64 %0, 16
+  %d = icmp ugt i64 %c, 1048575 ; 0x0f_ffff
+  ret i1 %d
+}
+
+define <2 x i1> @icmp_ule_i64x2(<2 x i64>) {
+; CHECK-LABEL: @icmp_ule_i64x2(
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc <2 x i64> %0 to <2 x i48>
+; CHECK-NEXT:    [[D:%.*]] = icmp eq <2 x i48> [[TMP2]], zeroinitializer
+; CHECK-NEXT:    ret <2 x i1> [[D]]
+;
+  %c = shl nuw <2 x i64> %0, <i64 16, i64 16>
+  %d = icmp ule <2 x i64> %c, <i64 65535, i64 65535>
+  ret <2 x i1> %d
+}
Index: lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1966,6 +1966,17 @@
     return new ICmpInst(Pred, Builder->CreateTrunc(X, TruncTy), NewC);
   }
 
+  // When the shift is nuw and pred is >u or <=u, comparison only really happens
+  // in the pre-shifted bits.
+  if (Shl->hasNoUnsignedWrap() &&
+      (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_ULE)) {
+    Type *CTy = IntegerType::get(Cmp.getContext(), C->getBitWidth());
+    if (X->getType()->isVectorTy())
+      CTy = VectorType::get(CTy, X->getType()->getVectorNumElements());
+    Value *NewC = ConstantInt::get(CTy, C->lshr(*ShiftAmt));
+    return new ICmpInst(Pred, X, NewC);
+  }
+
   return nullptr;
 }
 


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