[llvm] [ValueTracking] Handle `icmp pred (trunc X), C` in `computeKnownBitsFromCmp` (PR #82803)
via llvm-commits
llvm-commits at lists.llvm.org
Fri Feb 23 09:47:36 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-analysis
Author: Yingwei Zheng (dtcxzyw)
<details>
<summary>Changes</summary>
This patch handles the pattern `icmp pred (trunc X), C` in `computeKnownBitsFromCmp` to infer low bits of `X` from dominating conditions.
---
Full diff: https://github.com/llvm/llvm-project/pull/82803.diff
3 Files Affected:
- (modified) llvm/lib/Analysis/DomConditionCache.cpp (+2-1)
- (modified) llvm/lib/Analysis/ValueTracking.cpp (+16-4)
- (modified) llvm/test/Transforms/InstCombine/known-bits.ll (+124)
``````````diff
diff --git a/llvm/lib/Analysis/DomConditionCache.cpp b/llvm/lib/Analysis/DomConditionCache.cpp
index 274f3ff44b2a6f..b1d9cdff943b80 100644
--- a/llvm/lib/Analysis/DomConditionCache.cpp
+++ b/llvm/lib/Analysis/DomConditionCache.cpp
@@ -27,7 +27,8 @@ static void findAffectedValues(Value *Cond,
// Peek through unary operators to find the source of the condition.
Value *Op;
- if (match(I, m_PtrToInt(m_Value(Op)))) {
+ if (match(I,
+ m_CombineOr(m_PtrToInt(m_Value(Op)), m_Trunc(m_Value(Op))))) {
if (isa<Instruction>(Op) || isa<Argument>(Op))
Affected.push_back(Op);
}
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 04f317228b3ea7..dbac5bc8aa7626 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -717,10 +717,22 @@ static void computeKnownBitsFromCond(const Value *V, Value *Cond,
computeKnownBitsFromCond(V, B, Known, Depth + 1, SQ, Invert);
}
- if (auto *Cmp = dyn_cast<ICmpInst>(Cond))
- computeKnownBitsFromCmp(
- V, Invert ? Cmp->getInversePredicate() : Cmp->getPredicate(),
- Cmp->getOperand(0), Cmp->getOperand(1), Known, SQ);
+ if (auto *Cmp = dyn_cast<ICmpInst>(Cond)) {
+ ICmpInst::Predicate Pred =
+ Invert ? Cmp->getInversePredicate() : Cmp->getPredicate();
+ Value *LHS = Cmp->getOperand(0);
+ Value *RHS = Cmp->getOperand(1);
+
+ // Handle icmp pred (trunc V), C
+ if (match(LHS, m_Trunc(m_Specific(V)))) {
+ KnownBits DstKnown(LHS->getType()->getScalarSizeInBits());
+ computeKnownBitsFromCmp(LHS, Pred, LHS, RHS, DstKnown, SQ);
+ Known = Known.unionWith(DstKnown.anyext(Known.getBitWidth()));
+ return;
+ }
+
+ computeKnownBitsFromCmp(V, Pred, LHS, RHS, Known, SQ);
+ }
}
void llvm::computeKnownBitsFromContext(const Value *V, KnownBits &Known,
diff --git a/llvm/test/Transforms/InstCombine/known-bits.ll b/llvm/test/Transforms/InstCombine/known-bits.ll
index 246579cc4cd0c0..3581256131a270 100644
--- a/llvm/test/Transforms/InstCombine/known-bits.ll
+++ b/llvm/test/Transforms/InstCombine/known-bits.ll
@@ -284,5 +284,129 @@ exit:
ret i8 %or2
}
+define i32 @test_icmp_trunc1(i32 %x){
+; CHECK-LABEL: @test_icmp_trunc1(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[Y:%.*]] = trunc i32 [[X:%.*]] to i16
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i16 [[Y]], 7
+; CHECK-NEXT: br i1 [[CMP]], label [[THEN:%.*]], label [[ELSE:%.*]]
+; CHECK: then:
+; CHECK-NEXT: ret i32 7
+; CHECK: else:
+; CHECK-NEXT: ret i32 0
+;
+entry:
+ %y = trunc i32 %x to i16
+ %cmp = icmp eq i16 %y, 7
+ br i1 %cmp, label %then, label %else
+then:
+ %z = and i32 %x, 15
+ ret i32 %z
+else:
+ ret i32 0
+}
+
+define i64 @test_icmp_trunc2(i64 %x) {
+; CHECK-LABEL: @test_icmp_trunc2(
+; CHECK-NEXT: [[CONV:%.*]] = trunc i64 [[X:%.*]] to i32
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[CONV]], 12
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[SEXT:%.*]] = and i64 [[X]], 2147483647
+; CHECK-NEXT: ret i64 [[SEXT]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i64 0
+;
+ %conv = trunc i64 %x to i32
+ %cmp = icmp sgt i32 %conv, 12
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %sext = shl i64 %x, 32
+ %ret = ashr exact i64 %sext, 32
+ ret i64 %ret
+if.else:
+ ret i64 0
+}
+
+define i64 @test_icmp_trunc3(i64 %n) {
+; CHECK-LABEL: @test_icmp_trunc3(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[CONV:%.*]] = trunc i64 [[N:%.*]] to i32
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[CONV]], 96
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[RET:%.*]] = and i64 [[N]], 127
+; CHECK-NEXT: ret i64 [[RET]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i64 0
+;
+entry:
+ %conv = trunc i64 %n to i32
+ %cmp = icmp ult i32 %conv, 96
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %ret = and i64 %n, 4294967295
+ ret i64 %ret
+
+if.else:
+ ret i64 0
+}
+
+define i8 @test_icmp_trunc4(i64 %n) {
+; CHECK-LABEL: @test_icmp_trunc4(
+; CHECK-NEXT: [[CONV:%.*]] = trunc i64 [[N:%.*]] to i32
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[CONV]], 10
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[CONV2:%.*]] = trunc i64 [[N]] to i8
+; CHECK-NEXT: [[ADD:%.*]] = or disjoint i8 [[CONV2]], 48
+; CHECK-NEXT: ret i8 [[ADD]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i8 0
+;
+ %conv = trunc i64 %n to i32
+ %cmp = icmp ult i32 %conv, 10
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %conv2 = trunc i64 %n to i8
+ %add = add i8 %conv2, 48
+ ret i8 %add
+
+if.else:
+ ret i8 0
+}
+
+define i64 @test_icmp_trunc5(i64 %n) {
+; CHECK-LABEL: @test_icmp_trunc5(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[SHR:%.*]] = ashr i64 [[N:%.*]], 47
+; CHECK-NEXT: [[CONV1:%.*]] = trunc i64 [[SHR]] to i32
+; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i32 [[CONV1]], -13
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[TMP0:%.*]] = and i64 [[SHR]], 15
+; CHECK-NEXT: [[NOT:%.*]] = xor i64 [[TMP0]], 15
+; CHECK-NEXT: ret i64 [[NOT]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i64 13
+;
+entry:
+ %shr = ashr i64 %n, 47
+ %conv1 = trunc i64 %shr to i32
+ %cmp = icmp ugt i32 %conv1, -13
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %and = and i64 %shr, 4294967295
+ %not = xor i64 %and, 4294967295
+ ret i64 %not
+
+if.else:
+ ret i64 13
+}
+
declare void @use(i1)
declare void @sink(i8)
``````````
</details>
https://github.com/llvm/llvm-project/pull/82803
More information about the llvm-commits
mailing list