[llvm] [ValueTracking] AllowEphemerals for alignment assumptions. (PR #108632)
via llvm-commits
llvm-commits at lists.llvm.org
Fri Sep 13 12:33:18 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-analysis
Author: Florian Hahn (fhahn)
<details>
<summary>Changes</summary>
Allow AllowEphemerals in isValidAssumeForContext, as the CxtI might
be the producer of the pointer in the bundle. At the moment, align
assumptions aren't optimized away.
This allows using the assumption in the computeKnownBits call in
getConstantMultipleImpl.
We could extend the computeKnownBits API to allow callers to specify if
ephemerals are allowed, if the info from computeKnownBitsFromContext is
used to remove alignment assumptions.
---
Full diff: https://github.com/llvm/llvm-project/pull/108632.diff
2 Files Affected:
- (modified) llvm/lib/Analysis/ValueTracking.cpp (+4-1)
- (modified) llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll (+174-4)
``````````diff
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index ba3ba7cc98136d..2e1b512ad9b0ad 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -820,9 +820,12 @@ void llvm::computeKnownBitsFromContext(const Value *V, KnownBits &Known,
continue;
if (RetainedKnowledge RK = getKnowledgeFromBundle(
*I, I->bundle_op_info_begin()[Elem.Index])) {
+ // Allow AllowEphemerals in isValidAssumeForContext, as the CxtI might
+ // be the producer of the pointer in the bundle. At the moment, align
+ // assumptions aren't optimized away.
if (RK.WasOn == V && RK.AttrKind == Attribute::Alignment &&
isPowerOf2_64(RK.ArgValue) &&
- isValidAssumeForContext(I, Q.CxtI, Q.DT))
+ isValidAssumeForContext(I, Q.CxtI, Q.DT, /*AllowEphemerals*/ true))
Known.Zero.setLowBits(Log2_64(RK.ArgValue));
}
continue;
diff --git a/llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll b/llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
index 37d6584b1e85f1..476cbc74e4c092 100644
--- a/llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
+++ b/llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
@@ -1652,10 +1652,7 @@ exit:
ret void
}
-; TODO: It feels like we should be able to calculate the symbolic max
-; exit count for the loop.inc block here, in the same way as
-; ptr_induction_eq_1. The problem seems to be in howFarToZero when the
-; ControlsOnlyExit is set to false.
+; We are not able to compute exit counts, as %a and %b might not be multiples of 8.
define void @ptr_induction_early_exit_eq_1(ptr %a, ptr %b, ptr %c) {
; CHECK-LABEL: 'ptr_induction_early_exit_eq_1'
; CHECK-NEXT: Classifying expressions for: @ptr_induction_early_exit_eq_1
@@ -1693,6 +1690,179 @@ exit:
ret void
}
+; Variant of @ptr_induction_early_exit_eq_1 with alignment info via load metadata.
+define void @ptr_induction_early_exit_eq_1_with_align_on_load(ptr %a, ptr %b, ptr %c) {
+; CHECK-LABEL: 'ptr_induction_early_exit_eq_1_with_align_on_load'
+; CHECK-NEXT: Classifying expressions for: @ptr_induction_early_exit_eq_1_with_align_on_load
+; CHECK-NEXT: %a_ = load ptr, ptr %a, align 8, !align !0
+; CHECK-NEXT: --> %a_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
+; CHECK-NEXT: %b_ = load ptr, ptr %b, align 8, !align !0
+; CHECK-NEXT: --> %b_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
+; CHECK-NEXT: %ptr.iv = phi ptr [ %ptr.iv.next, %loop.inc ], [ %a_, %entry ]
+; CHECK-NEXT: --> {%a_,+,8}<nuw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT: %ld1 = load ptr, ptr %ptr.iv, align 8
+; CHECK-NEXT: --> %ld1 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
+; CHECK-NEXT: %ptr.iv.next = getelementptr inbounds i8, ptr %ptr.iv, i64 8
+; CHECK-NEXT: --> {(8 + %a_),+,8}<nw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT: Determining loop execution counts for: @ptr_induction_early_exit_eq_1_with_align_on_load
+; CHECK-NEXT: Loop %loop: <multiple exits> Unpredictable backedge-taken count.
+; CHECK-NEXT: exit count for loop: ***COULDNOTCOMPUTE***
+; CHECK-NEXT: exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+; CHECK-NEXT: Loop %loop: constant max backedge-taken count is i64 2305843009213693951
+; CHECK-NEXT: Loop %loop: symbolic max backedge-taken count is ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+; CHECK-NEXT: symbolic max exit count for loop: ***COULDNOTCOMPUTE***
+; CHECK-NEXT: symbolic max exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+;
+entry:
+ %a_ = load ptr, ptr %a, !align !{i64 8}
+ %b_ = load ptr, ptr %b, !align !{i64 8}
+ %cmp = icmp eq ptr %a_, %b_
+ br i1 %cmp, label %exit, label %loop
+
+loop:
+ %ptr.iv = phi ptr [ %ptr.iv.next, %loop.inc ], [ %a_, %entry ]
+ %ld1 = load ptr, ptr %ptr.iv, align 8
+ %earlyexitcond = icmp eq ptr %ld1, %c
+ br i1 %earlyexitcond, label %exit, label %loop.inc
+
+loop.inc:
+ %ptr.iv.next = getelementptr inbounds i8, ptr %ptr.iv, i64 8
+ %exitcond = icmp eq ptr %ptr.iv.next, %b_
+ br i1 %exitcond, label %exit, label %loop
+
+exit:
+ ret void
+}
+
+; Variant of @ptr_induction_early_exit_eq_1 with alignment info via arument attributes.
+define void @ptr_induction_early_exit_eq_1_with_align_on_arguments(ptr align 8 %a, ptr align 8 %b, ptr %c) {
+; CHECK-LABEL: 'ptr_induction_early_exit_eq_1_with_align_on_arguments'
+; CHECK-NEXT: Classifying expressions for: @ptr_induction_early_exit_eq_1_with_align_on_arguments
+; CHECK-NEXT: %ptr.iv = phi ptr [ %ptr.iv.next, %loop.inc ], [ %a, %entry ]
+; CHECK-NEXT: --> {%a,+,8}<nuw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT: %ld1 = load ptr, ptr %ptr.iv, align 8
+; CHECK-NEXT: --> %ld1 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
+; CHECK-NEXT: %ptr.iv.next = getelementptr inbounds i8, ptr %ptr.iv, i64 8
+; CHECK-NEXT: --> {(8 + %a),+,8}<nw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT: Determining loop execution counts for: @ptr_induction_early_exit_eq_1_with_align_on_arguments
+; CHECK-NEXT: Loop %loop: <multiple exits> Unpredictable backedge-taken count.
+; CHECK-NEXT: exit count for loop: ***COULDNOTCOMPUTE***
+; CHECK-NEXT: exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a to i64)) + (ptrtoint ptr %b to i64)) /u 8)
+; CHECK-NEXT: Loop %loop: constant max backedge-taken count is i64 2305843009213693951
+; CHECK-NEXT: Loop %loop: symbolic max backedge-taken count is ((-8 + (-1 * (ptrtoint ptr %a to i64)) + (ptrtoint ptr %b to i64)) /u 8)
+; CHECK-NEXT: symbolic max exit count for loop: ***COULDNOTCOMPUTE***
+; CHECK-NEXT: symbolic max exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a to i64)) + (ptrtoint ptr %b to i64)) /u 8)
+;
+entry:
+ %cmp = icmp eq ptr %a, %b
+ br i1 %cmp, label %exit, label %loop
+
+loop:
+ %ptr.iv = phi ptr [ %ptr.iv.next, %loop.inc ], [ %a, %entry ]
+ %ld1 = load ptr, ptr %ptr.iv, align 8
+ %earlyexitcond = icmp eq ptr %ld1, %c
+ br i1 %earlyexitcond, label %exit, label %loop.inc
+
+loop.inc:
+ %ptr.iv.next = getelementptr inbounds i8, ptr %ptr.iv, i64 8
+ %exitcond = icmp eq ptr %ptr.iv.next, %b
+ br i1 %exitcond, label %exit, label %loop
+
+exit:
+ ret void
+}
+
+; Variant of @ptr_induction_early_exit_eq_1 with alignment assumptions.
+define void @ptr_induction_early_exit_eq_1_align_assumption_1(ptr %a, ptr %b, ptr %c) {
+; CHECK-LABEL: 'ptr_induction_early_exit_eq_1_align_assumption_1'
+; CHECK-NEXT: Classifying expressions for: @ptr_induction_early_exit_eq_1_align_assumption_1
+; CHECK-NEXT: %a_ = load ptr, ptr %a, align 8
+; CHECK-NEXT: --> %a_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
+; CHECK-NEXT: %b_ = load ptr, ptr %b, align 8
+; CHECK-NEXT: --> %b_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
+; CHECK-NEXT: %ptr.iv = phi ptr [ %ptr.iv.next, %loop.inc ], [ %a_, %entry ]
+; CHECK-NEXT: --> {%a_,+,8}<nuw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT: %ld1 = load ptr, ptr %ptr.iv, align 8
+; CHECK-NEXT: --> %ld1 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
+; CHECK-NEXT: %ptr.iv.next = getelementptr inbounds i8, ptr %ptr.iv, i64 8
+; CHECK-NEXT: --> {(8 + %a_),+,8}<nw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT: Determining loop execution counts for: @ptr_induction_early_exit_eq_1_align_assumption_1
+; CHECK-NEXT: Loop %loop: <multiple exits> Unpredictable backedge-taken count.
+; CHECK-NEXT: exit count for loop: ***COULDNOTCOMPUTE***
+; CHECK-NEXT: exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+; CHECK-NEXT: Loop %loop: constant max backedge-taken count is i64 2305843009213693951
+; CHECK-NEXT: Loop %loop: symbolic max backedge-taken count is ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+; CHECK-NEXT: symbolic max exit count for loop: ***COULDNOTCOMPUTE***
+; CHECK-NEXT: symbolic max exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+;
+entry:
+ %a_ = load ptr, ptr %a
+ call void @llvm.assume(i1 true) [ "align"(ptr %a_, i64 8) ]
+ %b_ = load ptr, ptr %b
+ call void @llvm.assume(i1 true) [ "align"(ptr %b_, i64 8) ]
+ %cmp = icmp eq ptr %a_, %b_
+ br i1 %cmp, label %exit, label %loop
+
+loop:
+ %ptr.iv = phi ptr [ %ptr.iv.next, %loop.inc ], [ %a_, %entry ]
+ %ld1 = load ptr, ptr %ptr.iv, align 8
+ %earlyexitcond = icmp eq ptr %ld1, %c
+ br i1 %earlyexitcond, label %exit, label %loop.inc
+
+loop.inc:
+ %ptr.iv.next = getelementptr inbounds i8, ptr %ptr.iv, i64 8
+ %exitcond = icmp eq ptr %ptr.iv.next, %b_
+ br i1 %exitcond, label %exit, label %loop
+
+exit:
+ ret void
+}
+
+define void @ptr_induction_early_exit_eq_1_align_assumption_2(ptr %a, ptr %b, ptr %c) {
+; CHECK-LABEL: 'ptr_induction_early_exit_eq_1_align_assumption_2'
+; CHECK-NEXT: Classifying expressions for: @ptr_induction_early_exit_eq_1_align_assumption_2
+; CHECK-NEXT: %a_ = load ptr, ptr %a, align 8
+; CHECK-NEXT: --> %a_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
+; CHECK-NEXT: %b_ = load ptr, ptr %b, align 8
+; CHECK-NEXT: --> %b_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
+; CHECK-NEXT: %ptr.iv = phi ptr [ %ptr.iv.next, %loop.inc ], [ %a_, %entry ]
+; CHECK-NEXT: --> {%a_,+,8}<nuw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT: %ld1 = load ptr, ptr %ptr.iv, align 8
+; CHECK-NEXT: --> %ld1 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
+; CHECK-NEXT: %ptr.iv.next = getelementptr inbounds i8, ptr %ptr.iv, i64 8
+; CHECK-NEXT: --> {(8 + %a_),+,8}<nw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT: Determining loop execution counts for: @ptr_induction_early_exit_eq_1_align_assumption_2
+; CHECK-NEXT: Loop %loop: <multiple exits> Unpredictable backedge-taken count.
+; CHECK-NEXT: exit count for loop: ***COULDNOTCOMPUTE***
+; CHECK-NEXT: exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+; CHECK-NEXT: Loop %loop: constant max backedge-taken count is i64 2305843009213693951
+; CHECK-NEXT: Loop %loop: symbolic max backedge-taken count is ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+; CHECK-NEXT: symbolic max exit count for loop: ***COULDNOTCOMPUTE***
+; CHECK-NEXT: symbolic max exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+;
+entry:
+ %a_ = load ptr, ptr %a
+ %b_ = load ptr, ptr %b
+ call void @llvm.assume(i1 true) [ "align"(ptr %a_, i64 8) ]
+ call void @llvm.assume(i1 true) [ "align"(ptr %b_, i64 8) ]
+ %cmp = icmp eq ptr %a_, %b_
+ br i1 %cmp, label %exit, label %loop
+
+loop:
+ %ptr.iv = phi ptr [ %ptr.iv.next, %loop.inc ], [ %a_, %entry ]
+ %ld1 = load ptr, ptr %ptr.iv, align 8
+ %earlyexitcond = icmp eq ptr %ld1, %c
+ br i1 %earlyexitcond, label %exit, label %loop.inc
+
+loop.inc:
+ %ptr.iv.next = getelementptr inbounds i8, ptr %ptr.iv, i64 8
+ %exitcond = icmp eq ptr %ptr.iv.next, %b_
+ br i1 %exitcond, label %exit, label %loop
+
+exit:
+ ret void
+}
+
define void @ptr_induction_early_exit_eq_2(ptr %a, i64 %n, ptr %c) {
; CHECK-LABEL: 'ptr_induction_early_exit_eq_2'
; CHECK-NEXT: Classifying expressions for: @ptr_induction_early_exit_eq_2
``````````
</details>
https://github.com/llvm/llvm-project/pull/108632
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