[llvm] 77f2f34 - [InstCombine] Generalize (icmp sgt (1 << Y), -1) -> (icmp ne Y, BitWidth-1) to any negative constant.

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2023-01-15T13:36:57-08:00
New Revision: 77f2f34d696b77fe5bf05afbe7386966b6bcc8ba

URL: https://github.com/llvm/llvm-project/commit/77f2f34d696b77fe5bf05afbe7386966b6bcc8ba
DIFF: https://github.com/llvm/llvm-project/commit/77f2f34d696b77fe5bf05afbe7386966b6bcc8ba.diff

LOG: [InstCombine] Generalize (icmp sgt (1 << Y), -1) -> (icmp ne Y, BitWidth-1) to any negative constant.

Similar for the sle version which will be canonicalized to slt first.

Alive2 proof as implemented: https://alive2.llvm.org/ce/z/_YawdM

@spatel's  original Alive2: https://alive2.llvm.org/ce/z/3YB2vs

Reviewed By: lebedev.ri

Differential Revision: https://reviews.llvm.org/D141773

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 983e73e40fb36..6571c07ec752b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2047,15 +2047,15 @@ static Instruction *foldICmpShlOne(ICmpInst &Cmp, Instruction *Shl,
   } else if (Cmp.isSigned()) {
     Constant *BitWidthMinusOne = ConstantInt::get(ShiftType, TypeBits - 1);
     // (1 << Y) >  0 -> Y != 31
-    // (1 << Y) > -1 -> Y != 31
-    // TODO: This can be generalized to any negative constant.
-    if (Pred == ICmpInst::ICMP_SGT && (C.isZero() || C.isAllOnes()))
+    // (1 << Y) >  C -> Y != 31 if C is negative.
+    if (Pred == ICmpInst::ICMP_SGT && C.sle(0))
       return new ICmpInst(ICmpInst::ICMP_NE, Y, BitWidthMinusOne);
 
     // (1 << Y) <  0 -> Y == 31
     // (1 << Y) <  1 -> Y == 31
-    // TODO: This can be generalized to any negative constant except signed min.
-    if (Pred == ICmpInst::ICMP_SLT && (C.isZero() || C.isOne()))
+    // (1 << Y) <  C -> Y == 31 if C is negative and not signed min.
+    // Exclude signed min by subtracting 1 and lower the upper bound to 0.
+    if (Pred == ICmpInst::ICMP_SLT && (C-1).sle(0))
       return new ICmpInst(ICmpInst::ICMP_EQ, Y, BitWidthMinusOne);
   } else if (Cmp.isEquality() && CIsPowerOf2) {
     return new ICmpInst(Pred, Y, ConstantInt::get(ShiftType, C.logBase2()));

diff  --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
index 4643278dd291d..f98f05c55af66 100644
--- a/llvm/test/Transforms/InstCombine/icmp.ll
+++ b/llvm/test/Transforms/InstCombine/icmp.ll
@@ -2178,6 +2178,26 @@ define <2 x i1> @icmp_shl_1_V_sle_0_vec(<2 x i32> %V) {
   ret <2 x i1> %cmp
 }
 
+define i1 @icmp_shl_1_V_sle_negative(i32 %V) {
+; CHECK-LABEL: @icmp_shl_1_V_sle_negative(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[V:%.*]], 31
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %shl = shl i32 1, %V
+  %cmp = icmp sle i32 %shl, -42
+  ret i1 %cmp
+}
+
+define <2 x i1> @icmp_shl_1_V_sle_0_negative(<2 x i32> %V) {
+; CHECK-LABEL: @icmp_shl_1_V_sle_0_negative(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq <2 x i32> [[V:%.*]], <i32 31, i32 31>
+; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+;
+  %shl = shl <2 x i32> <i32 1, i32 1>, %V
+  %cmp = icmp sle <2 x i32> %shl, <i32 -2147483647, i32 -2147483647>
+  ret <2 x i1> %cmp
+}
+
 define i1 @icmp_shl_1_V_sgt_0(i32 %V) {
 ; CHECK-LABEL: @icmp_shl_1_V_sgt_0(
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i32 [[V:%.*]], 31
@@ -2198,6 +2218,26 @@ define <2 x i1> @icmp_shl_1_V_sgt_0_vec(<2 x i32> %V) {
   ret <2 x i1> %cmp
 }
 
+define i1 @icmp_shl_1_V_sgt_negative(i32 %V) {
+; CHECK-LABEL: @icmp_shl_1_V_sgt_negative(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i32 [[V:%.*]], 31
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %shl = shl i32 1, %V
+  %cmp = icmp sgt i32 %shl, -12345
+  ret i1 %cmp
+}
+
+define <2 x i1> @icmp_shl_1_V_sgt_negative_vec(<2 x i32> %V) {
+; CHECK-LABEL: @icmp_shl_1_V_sgt_negative_vec(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne <2 x i32> [[V:%.*]], <i32 31, i32 31>
+; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+;
+  %shl = shl <2 x i32> <i32 1, i32 1>, %V
+  %cmp = icmp sgt <2 x i32> %shl, <i32 -2, i32 -2>
+  ret <2 x i1> %cmp
+}
+
 define i1 @or_icmp_eq_B_0_icmp_ult_A_B(i64 %a, i64 %b) {
 ; CHECK-LABEL: @or_icmp_eq_B_0_icmp_ult_A_B(
 ; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[B:%.*]], -1