[llvm] [ValueTracking] Compute knownbits from `(icmp ult/ule (add nuw X, Y), C)` (PR #87180)
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Sun Mar 31 09:01:07 PDT 2024
https://github.com/goldsteinn updated https://github.com/llvm/llvm-project/pull/87180
>From 8d9ea7198937d88984732a5611f1778984c9f158 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Sat, 30 Mar 2024 21:38:23 -0500
Subject: [PATCH 1/2] [ValueTracking] Add tests for computing knownbits from
`(icmp ult/ule (add nuw X, Y), C)`; NFC
---
.../test/Transforms/InstCombine/known-bits.ll | 105 +++++++++++++++++-
1 file changed, 100 insertions(+), 5 deletions(-)
diff --git a/llvm/test/Transforms/InstCombine/known-bits.ll b/llvm/test/Transforms/InstCombine/known-bits.ll
index 5305c78f691231..fee2107995b728 100644
--- a/llvm/test/Transforms/InstCombine/known-bits.ll
+++ b/llvm/test/Transforms/InstCombine/known-bits.ll
@@ -124,7 +124,6 @@ exit:
ret i8 %or2
}
-
define i8 @test_cond_and_bothways(i8 %x) {
; CHECK-LABEL: @test_cond_and_bothways(
; CHECK-NEXT: [[AND:%.*]] = and i8 [[X:%.*]], 91
@@ -181,8 +180,6 @@ exit:
ret i8 %or2
}
-
-
define i8 @test_cond_and_commuted(i8 %x, i1 %c1, i1 %c2) {
; CHECK-LABEL: @test_cond_and_commuted(
; CHECK-NEXT: [[AND:%.*]] = and i8 [[X:%.*]], 3
@@ -343,7 +340,7 @@ exit:
ret i8 %or2
}
-define i32 @test_icmp_trunc1(i32 %x){
+define i32 @test_icmp_trunc1(i32 %x) {
; CHECK-LABEL: @test_icmp_trunc1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[Y:%.*]] = trunc i32 [[X:%.*]] to i16
@@ -365,7 +362,7 @@ else:
ret i32 0
}
-define i32 @test_icmp_trunc_assume(i32 %x){
+define i32 @test_icmp_trunc_assume(i32 %x) {
; CHECK-LABEL: @test_icmp_trunc_assume(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[Y:%.*]] = trunc i32 [[X:%.*]] to i16
@@ -532,7 +529,105 @@ if.else:
ret i1 %other
}
+define i8 @test_icmp_add(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_add(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_ADD:%.*]] = add nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[N_ADD]], 32
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+;
+entry:
+ %n_add = add nuw i8 %n, %n2
+ %cmp = icmp ult i8 %n_add, 32
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %r = and i8 %n, 32
+ ret i8 %r
+if.else:
+ ret i8 %other
+}
+
+define i8 @test_icmp_add2(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_add2(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_ADD:%.*]] = add nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i8 [[N_ADD]], 14
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+; CHECK: if.else:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+;
+entry:
+ %n_add = add nuw i8 %n, %n2
+ %cmp = icmp uge i8 %n_add, 15
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ ret i8 %other
+if.else:
+ %r = and i8 %n, 32
+ ret i8 %r
+
+}
+
+define i8 @test_icmp_add_fail_bad_range(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_add_fail_bad_range(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_ADD:%.*]] = add nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[N_ADD]], 33
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+;
+entry:
+ %n_add = add nuw i8 %n, %n2
+ %cmp = icmp ule i8 %n_add, 32
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %r = and i8 %n, 32
+ ret i8 %r
+
+if.else:
+ ret i8 %other
+}
+
+define i8 @test_icmp_add_fail_bad_pred(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_add_fail_bad_pred(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_ADD:%.*]] = add nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i8 [[N_ADD]], 32
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+;
+entry:
+ %n_add = add nuw i8 %n, %n2
+ %cmp = icmp ugt i8 %n_add, 32
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %r = and i8 %n, 32
+ ret i8 %r
+
+if.else:
+ ret i8 %other
+}
declare void @use(i1)
declare void @sink(i8)
>From 0341e8924a0063b86cbbd0292ccc70922297953a Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Sat, 30 Mar 2024 21:39:36 -0500
Subject: [PATCH 2/2] [ValueTracking] Compute knownbits from `(icmp ult/ule
(add nuw X, Y), C)`
`(icmp ule/ult (or X, Y), C)` implies both `(icmp ule/ult X, C)` and
`(icmp ule/ult Y, C)`. We can use this to deduce leading zeros in `X`.
Proofs: https://alive2.llvm.org/ce/z/ocvv5F
---
llvm/lib/Analysis/ValueTracking.cpp | 39 +++++++++++++------
.../test/Transforms/InstCombine/known-bits.ll | 6 +--
2 files changed, 29 insertions(+), 16 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index b5e8a1d22f264b..6b32180085d761 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -698,13 +698,19 @@ static void computeKnownBitsFromCmp(const Value *V, CmpInst::Predicate Pred,
break;
}
default:
- const APInt *Offset = nullptr;
- if (match(LHS, m_CombineOr(m_V, m_AddLike(m_V, m_APInt(Offset)))) &&
- match(RHS, m_APInt(C))) {
- ConstantRange LHSRange = ConstantRange::makeAllowedICmpRegion(Pred, *C);
- if (Offset)
- LHSRange = LHSRange.sub(*Offset);
- Known = Known.unionWith(LHSRange.toKnownBits());
+ if (match(RHS, m_APInt(C))) {
+ const APInt *Offset = nullptr;
+ if (match(LHS, m_CombineOr(m_V, m_AddLike(m_V, m_APInt(Offset))))) {
+ ConstantRange LHSRange = ConstantRange::makeAllowedICmpRegion(Pred, *C);
+ if (Offset)
+ LHSRange = LHSRange.sub(*Offset);
+ Known = Known.unionWith(LHSRange.toKnownBits());
+ }
+ if ((Pred == ICmpInst::ICMP_ULE || Pred == ICmpInst::ICMP_ULT) &&
+ match(LHS, m_c_NUWAdd(m_V, m_Value()))) {
+ Known.Zero.setHighBits(
+ (*C - (Pred == ICmpInst::ICMP_ULT)).countLeadingZeros());
+ }
}
break;
}
@@ -9283,11 +9289,20 @@ void llvm::findValuesAffectedByCondition(
AddAffected(X);
}
} else {
- // Handle (A + C1) u< C2, which is the canonical form of
- // A > C3 && A < C4.
- if (match(A, m_AddLike(m_Value(X), m_ConstantInt())) &&
- match(B, m_ConstantInt()))
- AddAffected(X);
+ if (match(B, m_ConstantInt())) {
+ // Handle (A + C1) u< C2, which is the canonical form of
+ // A > C3 && A < C4.
+ if (match(A, m_AddLike(m_Value(X), m_ConstantInt())))
+ AddAffected(X);
+
+ Value *Y;
+ // X nuw+ Y u< C -> X u< C && Y u< C
+ if (ICmpInst::isUnsigned(Pred) &&
+ match(A, m_NUWAdd(m_Value(X), m_Value(Y)))) {
+ AddAffected(X);
+ AddAffected(Y);
+ }
+ }
// Handle icmp slt/sgt (bitcast X to int), 0/-1, which is supported
// by computeKnownFPClass().
diff --git a/llvm/test/Transforms/InstCombine/known-bits.ll b/llvm/test/Transforms/InstCombine/known-bits.ll
index fee2107995b728..0ed63512f8cb49 100644
--- a/llvm/test/Transforms/InstCombine/known-bits.ll
+++ b/llvm/test/Transforms/InstCombine/known-bits.ll
@@ -536,8 +536,7 @@ define i8 @test_icmp_add(i8 %n, i8 %n2, i8 %other) {
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[N_ADD]], 32
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
-; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
-; CHECK-NEXT: ret i8 [[R]]
+; CHECK-NEXT: ret i8 0
; CHECK: if.else:
; CHECK-NEXT: ret i8 [[OTHER:%.*]]
;
@@ -563,8 +562,7 @@ define i8 @test_icmp_add2(i8 %n, i8 %n2, i8 %other) {
; CHECK: if.then:
; CHECK-NEXT: ret i8 [[OTHER:%.*]]
; CHECK: if.else:
-; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
-; CHECK-NEXT: ret i8 [[R]]
+; CHECK-NEXT: ret i8 0
;
entry:
%n_add = add nuw i8 %n, %n2
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