[llvm] [ValueTracking] Use select condition to help infer bits of arms (PR #84699)
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Mon Mar 11 07:44:56 PDT 2024
https://github.com/goldsteinn updated https://github.com/llvm/llvm-project/pull/84699
>From d204761fab275ef53ecc01f64fb72d3277c7d4c1 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Sun, 10 Mar 2024 17:24:09 -0500
Subject: [PATCH 1/2] [ValueTracking] Add tests for inferring select arm bits
from condition; NFC
---
.../knownbits-select-from-cond.ll | 66 +++++++++++++++++++
1 file changed, 66 insertions(+)
create mode 100644 llvm/test/Analysis/ValueTracking/knownbits-select-from-cond.ll
diff --git a/llvm/test/Analysis/ValueTracking/knownbits-select-from-cond.ll b/llvm/test/Analysis/ValueTracking/knownbits-select-from-cond.ll
new file mode 100644
index 00000000000000..bbeb352b9e063b
--- /dev/null
+++ b/llvm/test/Analysis/ValueTracking/knownbits-select-from-cond.ll
@@ -0,0 +1,66 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=instcombine -S < %s | FileCheck %s
+
+define i8 @select_condition_implies_highbits_op1(i8 %xx, i8 %y) {
+; CHECK-LABEL: @select_condition_implies_highbits_op1(
+; CHECK-NEXT: [[X:%.*]] = and i8 [[XX:%.*]], 15
+; CHECK-NEXT: [[COND:%.*]] = icmp ult i8 [[Y:%.*]], 3
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[Y]], i8 [[X]]
+; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
+; CHECK-NEXT: ret i8 [[R]]
+;
+ %x = and i8 %xx, 15
+ %cond = icmp ult i8 %y, 3
+ %sel = select i1 %cond, i8 %y, i8 %x
+ %r = add i8 %sel, 32
+ ret i8 %r
+}
+
+define i8 @select_condition_implies_highbits_op2(i8 %xx, i8 %y) {
+; CHECK-LABEL: @select_condition_implies_highbits_op2(
+; CHECK-NEXT: [[X:%.*]] = and i8 [[XX:%.*]], 15
+; CHECK-NEXT: [[COND:%.*]] = icmp ugt i8 [[Y:%.*]], 3
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[X]], i8 [[Y]]
+; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
+; CHECK-NEXT: ret i8 [[R]]
+;
+ %x = and i8 %xx, 15
+ %cond = icmp ugt i8 %y, 3
+ %sel = select i1 %cond, i8 %x, i8 %y
+ %r = add i8 %sel, 32
+ ret i8 %r
+}
+
+define i8 @select_condition_implies_highbits_op1_and(i8 %xx, i8 %y, i1 %other_cond) {
+; CHECK-LABEL: @select_condition_implies_highbits_op1_and(
+; CHECK-NEXT: [[X:%.*]] = and i8 [[XX:%.*]], 15
+; CHECK-NEXT: [[COND0:%.*]] = icmp ult i8 [[Y:%.*]], 3
+; CHECK-NEXT: [[COND:%.*]] = and i1 [[COND0]], [[OTHER_COND:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[Y]], i8 [[X]]
+; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
+; CHECK-NEXT: ret i8 [[R]]
+;
+ %x = and i8 %xx, 15
+ %cond0 = icmp ult i8 %y, 3
+ %cond = and i1 %cond0, %other_cond
+ %sel = select i1 %cond, i8 %y, i8 %x
+ %r = add i8 %sel, 32
+ ret i8 %r
+}
+
+define i8 @select_condition_implies_highbits_op2_or(i8 %xx, i8 %y, i1 %other_cond) {
+; CHECK-LABEL: @select_condition_implies_highbits_op2_or(
+; CHECK-NEXT: [[X:%.*]] = and i8 [[XX:%.*]], 15
+; CHECK-NEXT: [[COND0:%.*]] = icmp ugt i8 [[Y:%.*]], 3
+; CHECK-NEXT: [[COND:%.*]] = or i1 [[COND0]], [[OTHER_COND:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[X]], i8 [[Y]]
+; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
+; CHECK-NEXT: ret i8 [[R]]
+;
+ %x = and i8 %xx, 15
+ %cond0 = icmp ugt i8 %y, 3
+ %cond = or i1 %cond0, %other_cond
+ %sel = select i1 %cond, i8 %x, i8 %y
+ %r = add i8 %sel, 32
+ ret i8 %r
+}
>From 0310ed027f39316481f52adabea171a9db8da36f Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Sun, 10 Mar 2024 17:24:12 -0500
Subject: [PATCH 2/2] [ValueTracking] Use select condition to help infer bits
of arms
If we have something like `(select (icmp ult x, 8), x, y)`, we can use
the `(icmp ult x, 8)` to help compute the knownbits of `x`.
---
llvm/lib/Analysis/ValueTracking.cpp | 27 ++++++++++++++++---
.../ScalarEvolution/max-expr-cache.ll | 12 ++++-----
.../knownbits-select-from-cond.ll | 8 +++---
3 files changed, 33 insertions(+), 14 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 6d0e79e11eed43..65dfc13c22dbce 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1023,11 +1023,30 @@ static void computeKnownBitsFromOperator(const Operator *I,
break;
}
case Instruction::Select: {
- computeKnownBits(I->getOperand(2), Known, Depth + 1, Q);
- computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
-
+ auto ComputeForArm = [&](bool Arm) {
+ unsigned ArmIdx = 1 + static_cast<unsigned>(!Arm);
+ KnownBits Res(Known.getBitWidth());
+ computeKnownBits(I->getOperand(ArmIdx), Res, Depth + 1, Q);
+ // See what condition implies about the bits of the two select arms.
+ if (!Known.isConstant()) {
+ KnownBits KnownFromCond(Known.getBitWidth());
+ computeKnownBitsFromCond(I->getOperand(ArmIdx), I->getOperand(0),
+ KnownFromCond, Depth + 1, Q, !Arm);
+ KnownFromCond = KnownFromCond.unionWith(Res);
+ // We can have conflict if the condition is dead. I.e if we have
+ // (x | 64) < 32 ? (x | 64) : y
+ // we will have conflict at bit 6 from the condition/the `or`.
+ // In that case, we just ignore the bits from the condition. Its not
+ // particularly important what we do, as this select is going to be
+ // simplified soon.
+ if (!KnownFromCond.hasConflict())
+ Res = KnownFromCond;
+ }
+ return Res;
+ };
// Only known if known in both the LHS and RHS.
- Known = Known.intersectWith(Known2);
+ Known =
+ ComputeForArm(/*Arm=*/true).intersectWith(ComputeForArm(/*Arm=*/false));
break;
}
case Instruction::FPTrunc:
diff --git a/llvm/test/Analysis/ScalarEvolution/max-expr-cache.ll b/llvm/test/Analysis/ScalarEvolution/max-expr-cache.ll
index e1c05c4b431f39..c9128522efcdaa 100644
--- a/llvm/test/Analysis/ScalarEvolution/max-expr-cache.ll
+++ b/llvm/test/Analysis/ScalarEvolution/max-expr-cache.ll
@@ -226,21 +226,21 @@ define void @umax(i32 %tmp3) {
; CHECK-NEXT: %tmp48 = select i1 %tmp47, i32 %tmp44, i32 %tmp46
; CHECK-NEXT: --> ((7 + (256 umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umax (256 umin (1 + (256 umin (1 + (256 umin (1 + (256 umin (1 + (256 umin (1 + (256 umin (1 + (256 umin (1 + (256 umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>))<nuw><nsw> umin {%tmp3,+,-256}<%bb4>)) U: [7,264) S: [7,264) Exits: <<Unknown>> LoopDispositions: { %bb4: Computable, %bb53: Invariant }
; CHECK-NEXT: %tmp49 = ashr i32 %tmp48, 3
-; CHECK-NEXT: --> %tmp49 U: [-268435456,268435456) S: [-268435456,268435456) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
+; CHECK-NEXT: --> %tmp49 U: [0,128) S: [0,128) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
; CHECK-NEXT: %tmp51 = select i1 %tmp50, i32 %tmp49, i32 0
-; CHECK-NEXT: --> %tmp49 U: [-268435456,268435456) S: [-268435456,268435456) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
+; CHECK-NEXT: --> %tmp49 U: [0,128) S: [0,128) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
; CHECK-NEXT: %tmp52 = zext i32 %tmp51 to i64
-; CHECK-NEXT: --> (zext i32 %tmp49 to i64) U: [0,4294967296) S: [0,4294967296) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
+; CHECK-NEXT: --> (zext i32 %tmp49 to i64) U: [0,128) S: [0,128) Exits: <<Unknown>> LoopDispositions: { %bb4: Variant, %bb53: Invariant }
; CHECK-NEXT: %tmp54 = phi i64 [ undef, %bb4 ], [ %tmp59, %bb53 ]
; CHECK-NEXT: --> {undef,+,1}<nsw><%bb53> U: full-set S: full-set Exits: (-1 + (zext i32 %tmp49 to i64))<nsw> LoopDispositions: { %bb53: Computable, %bb4: Variant }
; CHECK-NEXT: %tmp55 = trunc i64 %tmp54 to i32
; CHECK-NEXT: --> {(trunc i64 undef to i32),+,1}<%bb53> U: full-set S: full-set Exits: (-1 + %tmp49)<nsw> LoopDispositions: { %bb53: Computable, %bb4: Variant }
; CHECK-NEXT: %tmp56 = shl nsw i32 %tmp55, 3
-; CHECK-NEXT: --> {(8 * (trunc i64 undef to i32)),+,8}<%bb53> U: [0,-7) S: [-2147483648,2147483641) Exits: (-8 + (8 * %tmp49)<nsw>) LoopDispositions: { %bb53: Computable, %bb4: Variant }
+; CHECK-NEXT: --> {(8 * (trunc i64 undef to i32)),+,8}<%bb53> U: [0,-7) S: [-2147483648,2147483641) Exits: (-8 + (8 * %tmp49)<nuw><nsw>)<nsw> LoopDispositions: { %bb53: Computable, %bb4: Variant }
; CHECK-NEXT: %tmp57 = sext i32 %tmp56 to i64
-; CHECK-NEXT: --> (sext i32 {(8 * (trunc i64 undef to i32)),+,8}<%bb53> to i64) U: [0,-7) S: [-2147483648,2147483641) Exits: (sext i32 (-8 + (8 * %tmp49)<nsw>) to i64) LoopDispositions: { %bb53: Computable, %bb4: Variant }
+; CHECK-NEXT: --> (sext i32 {(8 * (trunc i64 undef to i32)),+,8}<%bb53> to i64) U: [0,-7) S: [-2147483648,2147483641) Exits: (-8 + (8 * (zext i32 %tmp49 to i64))<nuw><nsw>)<nsw> LoopDispositions: { %bb53: Computable, %bb4: Variant }
; CHECK-NEXT: %tmp58 = getelementptr inbounds i8, ptr null, i64 %tmp57
-; CHECK-NEXT: --> ((sext i32 {(8 * (trunc i64 undef to i32)),+,8}<%bb53> to i64) + null) U: [0,-7) S: [-2147483648,2147483641) Exits: ((sext i32 (-8 + (8 * %tmp49)<nsw>) to i64) + null) LoopDispositions: { %bb53: Computable, %bb4: Variant }
+; CHECK-NEXT: --> ((sext i32 {(8 * (trunc i64 undef to i32)),+,8}<%bb53> to i64) + null) U: [0,-7) S: [-2147483648,2147483641) Exits: (-8 + (8 * (zext i32 %tmp49 to i64))<nuw><nsw> + null) LoopDispositions: { %bb53: Computable, %bb4: Variant }
; CHECK-NEXT: %tmp59 = add nsw i64 %tmp54, 1
; CHECK-NEXT: --> {(1 + undef),+,1}<nsw><%bb53> U: full-set S: full-set Exits: (zext i32 %tmp49 to i64) LoopDispositions: { %bb53: Computable, %bb4: Variant }
; CHECK-NEXT: %tmp62 = add nuw nsw i64 %tmp5, 1
diff --git a/llvm/test/Analysis/ValueTracking/knownbits-select-from-cond.ll b/llvm/test/Analysis/ValueTracking/knownbits-select-from-cond.ll
index bbeb352b9e063b..edf499cc96020e 100644
--- a/llvm/test/Analysis/ValueTracking/knownbits-select-from-cond.ll
+++ b/llvm/test/Analysis/ValueTracking/knownbits-select-from-cond.ll
@@ -6,7 +6,7 @@ define i8 @select_condition_implies_highbits_op1(i8 %xx, i8 %y) {
; CHECK-NEXT: [[X:%.*]] = and i8 [[XX:%.*]], 15
; CHECK-NEXT: [[COND:%.*]] = icmp ult i8 [[Y:%.*]], 3
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[Y]], i8 [[X]]
-; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
+; CHECK-NEXT: [[R:%.*]] = or disjoint i8 [[SEL]], 32
; CHECK-NEXT: ret i8 [[R]]
;
%x = and i8 %xx, 15
@@ -21,7 +21,7 @@ define i8 @select_condition_implies_highbits_op2(i8 %xx, i8 %y) {
; CHECK-NEXT: [[X:%.*]] = and i8 [[XX:%.*]], 15
; CHECK-NEXT: [[COND:%.*]] = icmp ugt i8 [[Y:%.*]], 3
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[X]], i8 [[Y]]
-; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
+; CHECK-NEXT: [[R:%.*]] = or disjoint i8 [[SEL]], 32
; CHECK-NEXT: ret i8 [[R]]
;
%x = and i8 %xx, 15
@@ -37,7 +37,7 @@ define i8 @select_condition_implies_highbits_op1_and(i8 %xx, i8 %y, i1 %other_co
; CHECK-NEXT: [[COND0:%.*]] = icmp ult i8 [[Y:%.*]], 3
; CHECK-NEXT: [[COND:%.*]] = and i1 [[COND0]], [[OTHER_COND:%.*]]
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[Y]], i8 [[X]]
-; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
+; CHECK-NEXT: [[R:%.*]] = or disjoint i8 [[SEL]], 32
; CHECK-NEXT: ret i8 [[R]]
;
%x = and i8 %xx, 15
@@ -54,7 +54,7 @@ define i8 @select_condition_implies_highbits_op2_or(i8 %xx, i8 %y, i1 %other_con
; CHECK-NEXT: [[COND0:%.*]] = icmp ugt i8 [[Y:%.*]], 3
; CHECK-NEXT: [[COND:%.*]] = or i1 [[COND0]], [[OTHER_COND:%.*]]
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], i8 [[X]], i8 [[Y]]
-; CHECK-NEXT: [[R:%.*]] = add i8 [[SEL]], 32
+; CHECK-NEXT: [[R:%.*]] = or disjoint i8 [[SEL]], 32
; CHECK-NEXT: ret i8 [[R]]
;
%x = and i8 %xx, 15
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