[llvm] 9885505 - [InstCombine] reduce icmp_eq0-of-and-of-select-of-constants
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 30 13:19:08 PST 2023
Author: Sanjay Patel
Date: 2023-01-30T16:17:15-05:00
New Revision: 98855059674cf1b6b415f8c543f2a923771fed27
URL: https://github.com/llvm/llvm-project/commit/98855059674cf1b6b415f8c543f2a923771fed27
DIFF: https://github.com/llvm/llvm-project/commit/98855059674cf1b6b415f8c543f2a923771fed27.diff
LOG: [InstCombine] reduce icmp_eq0-of-and-of-select-of-constants
This is the most basic patch to handle fixing issue #57666.
D133919 proposes to handle much more than this in a single patch,
but I've used 10 regression tests just to make sure this part is
doing what I expected and nothing more, and it already shows even
more potential TODO items.
The more general proofs from D133919 are correct, but I want to
enable this in smaller steps to reduce risk:
https://alive2.llvm.org/ce/z/RrVEyX
Differential Revision: https://reviews.llvm.org/D142847
Added:
Modified:
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
llvm/test/Transforms/InstCombine/icmp-select.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 5e0dac772a4f..8ff75d5e71aa 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1888,6 +1888,25 @@ Instruction *InstCombinerImpl::foldICmpAndConstant(ICmpInst &Cmp,
return new ICmpInst(NewPred, X, SubOne(cast<Constant>(Cmp.getOperand(1))));
}
+ // If we are testing the intersection of 2 select-of-nonzero-constants with no
+ // common bits set, it's the same as checking if exactly one select condition
+ // is set:
+ // ((A ? TC : FC) & (B ? TC : FC)) == 0 --> xor A, B
+ // TODO: Generalize for non-constant values.
+ // TODO: Invert with a "ne" predicate.
+ // TODO: Handle signed/unsigned predicates.
+ // TODO: Handle other bitwise logic connectors.
+ // TODO: Extend to handle a non-zero compare constant.
+ if (Pred == CmpInst::ICMP_EQ && C.isZero()) {
+ Value *A, *B;
+ const APInt *TC, *FC;
+ if (match(X, m_Select(m_Value(A), m_APInt(TC), m_APInt(FC))) &&
+ match(Y,
+ m_Select(m_Value(B), m_SpecificInt(*TC), m_SpecificInt(*FC))) &&
+ !TC->isZero() && !FC->isZero() && !TC->intersects(*FC))
+ return BinaryOperator::CreateXor(A, B);
+ }
+
// ((zext i1 X) & Y) == 0 --> !((trunc Y) & X)
// ((zext i1 X) & Y) != 0 --> ((trunc Y) & X)
// ((zext i1 X) & Y) == 1 --> ((trunc Y) & X)
diff --git a/llvm/test/Transforms/InstCombine/icmp-select.ll b/llvm/test/Transforms/InstCombine/icmp-select.ll
index 0c7b14531e68..315a22ebcd79 100644
--- a/llvm/test/Transforms/InstCombine/icmp-select.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-select.ll
@@ -262,10 +262,7 @@ define i1 @umin_seq_comparison(i8 %x, i8 %y) {
define i1 @select_constants_and_icmp_eq0(i1 %x, i1 %y) {
; CHECK-LABEL: @select_constants_and_icmp_eq0(
-; CHECK-NEXT: [[S1:%.*]] = select i1 [[X:%.*]], i8 2, i8 1
-; CHECK-NEXT: [[S2:%.*]] = select i1 [[Y:%.*]], i8 2, i8 1
-; CHECK-NEXT: [[AND:%.*]] = and i8 [[S1]], [[S2]]
-; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[AND]], 0
+; CHECK-NEXT: [[CMP:%.*]] = xor i1 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%s1 = select i1 %x, i8 2, i8 1
@@ -275,6 +272,8 @@ define i1 @select_constants_and_icmp_eq0(i1 %x, i1 %y) {
ret i1 %cmp
}
+; extra uses on all intermediates are ok
+
define i1 @select_constants_and_icmp_eq0_uses(i1 %x, i1 %y) {
; CHECK-LABEL: @select_constants_and_icmp_eq0_uses(
; CHECK-NEXT: [[S1:%.*]] = select i1 [[X:%.*]], i8 2, i8 1
@@ -283,7 +282,7 @@ define i1 @select_constants_and_icmp_eq0_uses(i1 %x, i1 %y) {
; CHECK-NEXT: call void @use(i8 [[S2]])
; CHECK-NEXT: [[AND:%.*]] = and i8 [[S1]], [[S2]]
; CHECK-NEXT: call void @use(i8 [[AND]])
-; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[AND]], 0
+; CHECK-NEXT: [[CMP:%.*]] = xor i1 [[X]], [[Y]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%s1 = select i1 %x, i8 2, i8 1
@@ -296,12 +295,11 @@ define i1 @select_constants_and_icmp_eq0_uses(i1 %x, i1 %y) {
ret i1 %cmp
}
+; vector splat constants are ok
+
define <2 x i1> @select_constants_and_icmp_eq0_vec_splat(<2 x i1> %x, <2 x i1> %y) {
; CHECK-LABEL: @select_constants_and_icmp_eq0_vec_splat(
-; CHECK-NEXT: [[S1:%.*]] = select <2 x i1> [[X:%.*]], <2 x i9> <i9 3, i9 3>, <2 x i9> <i9 48, i9 48>
-; CHECK-NEXT: [[S2:%.*]] = select <2 x i1> [[Y:%.*]], <2 x i9> <i9 3, i9 3>, <2 x i9> <i9 48, i9 48>
-; CHECK-NEXT: [[AND:%.*]] = and <2 x i9> [[S1]], [[S2]]
-; CHECK-NEXT: [[CMP:%.*]] = icmp eq <2 x i9> [[AND]], zeroinitializer
+; CHECK-NEXT: [[CMP:%.*]] = xor <2 x i1> [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%s1 = select <2 x i1> %x, <2 x i9> <i9 3, i9 3>, <2 x i9> <i9 48, i9 48>
@@ -311,6 +309,8 @@ define <2 x i1> @select_constants_and_icmp_eq0_vec_splat(<2 x i1> %x, <2 x i1> %
ret <2 x i1> %cmp
}
+; common bit set - simplified via known bits
+
define i1 @select_constants_and_icmp_eq0_common_bit(i1 %x, i1 %y) {
; CHECK-LABEL: @select_constants_and_icmp_eq0_common_bit(
; CHECK-NEXT: ret i1 false
@@ -322,6 +322,8 @@ define i1 @select_constants_and_icmp_eq0_common_bit(i1 %x, i1 %y) {
ret i1 %cmp
}
+; negative test - need matching constants
+
define i1 @select_constants_and_icmp_eq0_no_common_op1(i1 %x, i1 %y) {
; CHECK-LABEL: @select_constants_and_icmp_eq0_no_common_op1(
; CHECK-NEXT: [[S1:%.*]] = select i1 [[X:%.*]], i8 16, i8 3
@@ -337,6 +339,8 @@ define i1 @select_constants_and_icmp_eq0_no_common_op1(i1 %x, i1 %y) {
ret i1 %cmp
}
+; negative test - need matching constants
+
define i1 @select_constants_and_icmp_eq0_no_common_op2(i1 %x, i1 %y) {
; CHECK-LABEL: @select_constants_and_icmp_eq0_no_common_op2(
; CHECK-NEXT: [[S1:%.*]] = select i1 [[X:%.*]], i8 16, i8 3
@@ -352,6 +356,8 @@ define i1 @select_constants_and_icmp_eq0_no_common_op2(i1 %x, i1 %y) {
ret i1 %cmp
}
+; reduces via FoldOpInstSelect, but this could be a simple 'or'
+
define i1 @select_constants_and_icmp_eq0_zero_tval(i1 %x, i1 %y) {
; CHECK-LABEL: @select_constants_and_icmp_eq0_zero_tval(
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[X:%.*]], i1 true, i1 [[Y:%.*]]
@@ -364,6 +370,8 @@ define i1 @select_constants_and_icmp_eq0_zero_tval(i1 %x, i1 %y) {
ret i1 %cmp
}
+; reduces via FoldOpInstSelect, but this could be a simple 'not-of-and'
+
define i1 @select_constants_and_icmp_eq0_zero_fval(i1 %x, i1 %y) {
; CHECK-LABEL: @select_constants_and_icmp_eq0_zero_fval(
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[X:%.*]], i1 [[Y:%.*]], i1 false
@@ -377,6 +385,8 @@ define i1 @select_constants_and_icmp_eq0_zero_fval(i1 %x, i1 %y) {
ret i1 %cmp
}
+; TODO: x & y
+
define i1 @select_constants_and_icmp_eq_tval(i1 %x, i1 %y) {
; CHECK-LABEL: @select_constants_and_icmp_eq_tval(
; CHECK-NEXT: [[S1:%.*]] = select i1 [[X:%.*]], i8 6, i8 1
@@ -392,6 +402,8 @@ define i1 @select_constants_and_icmp_eq_tval(i1 %x, i1 %y) {
ret i1 %cmp
}
+; TODO: ~(x | y)
+
define i1 @select_constants_and_icmp_eq_fval(i1 %x, i1 %y) {
; CHECK-LABEL: @select_constants_and_icmp_eq_fval(
; CHECK-NEXT: [[S1:%.*]] = select i1 [[X:%.*]], i8 12, i8 3
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