[llvm] ValueTracking: simplify udiv/urem recurrences (PR #108973)
Ramkumar Ramachandra via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 21 11:59:53 PDT 2024
https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/108973
>From 6e66d098c7b0acecd8375d7d5261ab598f21a820 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Tue, 17 Sep 2024 12:25:25 +0100
Subject: [PATCH 1/2] ValueTracking: pre-commit tests for Div/Rem recurrence
---
.../ValueTracking/recurrence-knownbits.ll | 69 +++++++++++++++++++
1 file changed, 69 insertions(+)
diff --git a/llvm/test/Analysis/ValueTracking/recurrence-knownbits.ll b/llvm/test/Analysis/ValueTracking/recurrence-knownbits.ll
index 3355328cad9ecf0..726b52271c6afbe 100644
--- a/llvm/test/Analysis/ValueTracking/recurrence-knownbits.ll
+++ b/llvm/test/Analysis/ValueTracking/recurrence-knownbits.ll
@@ -81,6 +81,75 @@ exit:
ret i64 %res
}
+define i64 @test_udiv(i1 %c) {
+; CHECK-LABEL: @test_udiv(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[LOOP:%.*]]
+; CHECK: loop:
+; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 9, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT: [[IV_NEXT]] = udiv i64 [[IV]], 3
+; CHECK-NEXT: br i1 [[C:%.*]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK: exit:
+; CHECK-NEXT: [[RES:%.*]] = and i64 [[IV]], 16
+; CHECK-NEXT: ret i64 [[RES]]
+;
+entry:
+ br label %loop
+loop:
+ %iv = phi i64 [9, %entry], [%iv.next, %loop]
+ %iv.next = udiv i64 %iv, 3
+ br i1 %c, label %exit, label %loop
+exit:
+ %res = and i64 %iv, 16
+ ret i64 %res
+}
+
+define i64 @test_udiv_neg(i1 %c) {
+; CHECK-LABEL: @test_udiv_neg(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[LOOP:%.*]]
+; CHECK: loop:
+; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 2, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT: [[IV_NEXT]] = udiv i64 9, [[IV]]
+; CHECK-NEXT: br i1 [[C:%.*]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK: exit:
+; CHECK-NEXT: [[RES:%.*]] = and i64 [[IV]], 4
+; CHECK-NEXT: ret i64 [[RES]]
+;
+entry:
+ br label %loop
+loop:
+ %iv = phi i64 [2, %entry], [%iv.next, %loop]
+ %iv.next = udiv i64 9, %iv
+ br i1 %c, label %exit, label %loop
+exit:
+ %res = and i64 %iv, 4
+ ret i64 %res
+}
+
+define i64 @test_urem(i1 %c) {
+; CHECK-LABEL: @test_urem(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[LOOP:%.*]]
+; CHECK: loop:
+; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 3, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT: [[IV_NEXT]] = urem i64 9, [[IV]]
+; CHECK-NEXT: br i1 [[C:%.*]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK: exit:
+; CHECK-NEXT: [[RES:%.*]] = and i64 [[IV]], 4
+; CHECK-NEXT: ret i64 [[RES]]
+;
+entry:
+ br label %loop
+loop:
+ %iv = phi i64 [3, %entry], [%iv.next, %loop]
+ %iv.next = urem i64 9, %iv
+ br i1 %c, label %exit, label %loop
+exit:
+ %res = and i64 %iv, 4
+ ret i64 %res
+}
+
define i64 @test_and(i1 %c) {
; CHECK-LABEL: @test_and(
; CHECK-NEXT: entry:
>From ce712741a9b5778c48bc48b63a5b8c77d733c6d2 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Mon, 7 Oct 2024 10:39:08 +0100
Subject: [PATCH 2/2] ValueTracking: simplify udiv/urem recurrences
udiv and urem recurrences have the property that the result can never
exceed the start value. Implement a simplification based on this
property.
---
llvm/lib/Analysis/ValueTracking.cpp | 26 ++++++++++++++++++-
.../ValueTracking/recurrence-knownbits.ll | 10 ++-----
2 files changed, 27 insertions(+), 9 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index e9ed8b3c862b555..8bf10389447b20b 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1543,6 +1543,28 @@ static void computeKnownBitsFromOperator(const Operator *I,
}
break;
}
+
+ case Instruction::UDiv:
+ // For UDiv, the result can never exceed either the numerator, or the
+ // start value, whichever is greater. The case where the PHI is not
+ // the numerator of the UDiv is already handled by other code.
+ if (BO->getOperand(0) != P)
+ break;
+ [[fallthrough]];
+
+ case Instruction::URem: {
+ // For URem, the result can never exceed the start value.
+ SimplifyQuery RecQ = Q.getWithoutCondContext();
+
+ unsigned OpNum = P->getOperand(0) == R ? 0 : 1;
+ Instruction *RInst = P->getIncomingBlock(OpNum)->getTerminator();
+
+ RecQ.CxtI = RInst;
+ computeKnownBits(R, DemandedElts, Known2, Depth + 1, RecQ);
+ Known.Zero.setHighBits(Known2.countMinLeadingZeros());
+ break;
+ }
+
default:
break;
}
@@ -9010,12 +9032,14 @@ bool llvm::matchSimpleRecurrence(const PHINode *P, BinaryOperator *&BO,
switch (Opcode) {
default:
continue;
- // TODO: Expand list -- xor, div, gep, uaddo, etc..
+ // TODO: Expand list -- xor, gep, uadd.sat etc.
case Instruction::LShr:
case Instruction::AShr:
case Instruction::Shl:
case Instruction::Add:
case Instruction::Sub:
+ case Instruction::UDiv:
+ case Instruction::URem:
case Instruction::And:
case Instruction::Or:
case Instruction::Mul:
diff --git a/llvm/test/Analysis/ValueTracking/recurrence-knownbits.ll b/llvm/test/Analysis/ValueTracking/recurrence-knownbits.ll
index 726b52271c6afbe..2907266fe26333a 100644
--- a/llvm/test/Analysis/ValueTracking/recurrence-knownbits.ll
+++ b/llvm/test/Analysis/ValueTracking/recurrence-knownbits.ll
@@ -86,12 +86,9 @@ define i64 @test_udiv(i1 %c) {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
-; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 9, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
-; CHECK-NEXT: [[IV_NEXT]] = udiv i64 [[IV]], 3
; CHECK-NEXT: br i1 [[C:%.*]], label [[EXIT:%.*]], label [[LOOP]]
; CHECK: exit:
-; CHECK-NEXT: [[RES:%.*]] = and i64 [[IV]], 16
-; CHECK-NEXT: ret i64 [[RES]]
+; CHECK-NEXT: ret i64 0
;
entry:
br label %loop
@@ -132,12 +129,9 @@ define i64 @test_urem(i1 %c) {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
-; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 3, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
-; CHECK-NEXT: [[IV_NEXT]] = urem i64 9, [[IV]]
; CHECK-NEXT: br i1 [[C:%.*]], label [[EXIT:%.*]], label [[LOOP]]
; CHECK: exit:
-; CHECK-NEXT: [[RES:%.*]] = and i64 [[IV]], 4
-; CHECK-NEXT: ret i64 [[RES]]
+; CHECK-NEXT: ret i64 0
;
entry:
br label %loop
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