[PATCH] D113578: [SCEV] Apply loop guards when computing max BTC for arbitrary steps.
Florian Hahn via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Wed Nov 17 03:01:16 PST 2021
This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rGe8b55cf7b70a: [SCEV] Apply loop guards when computing max BTC for arbitrary steps. (authored by fhahn).
Changed prior to commit:
https://reviews.llvm.org/D113578?vs=387552&id=387887#toc
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D113578/new/
https://reviews.llvm.org/D113578
Files:
llvm/lib/Analysis/ScalarEvolution.cpp
llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info-rewrite-expressions.ll
Index: llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info-rewrite-expressions.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info-rewrite-expressions.ll
+++ llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info-rewrite-expressions.ll
@@ -64,12 +64,13 @@
ret i32 0
}
-; Test case from PR52464.
-define i32 @rewrite_zext_icmp_ne(i32 %N) {
-; CHECK-LABEL: Determining loop execution counts for: @rewrite_zext_icmp_ne
-; CHECK-NEXT: Loop %loop: backedge-taken count is ((-4 + (4 * ((4 + (zext i32 (-1 + (zext i2 (trunc i32 %N to i2) to i32))<nsw> to i64))<nuw><nsw> /u 4))<nuw><nsw>)<nsw> /u 4)
-; CHECK-NEXT: Loop %loop: max backedge-taken count is 1073741823
-; CHECK-NEXT: Loop %loop: Predicated backedge-taken count is ((-4 + (4 * ((4 + (zext i32 (-1 + (zext i2 (trunc i32 %N to i2) to i32))<nsw> to i64))<nuw><nsw> /u 4))<nuw><nsw>)<nsw> /u 4)
+; Test case from PR52464. applyLoopGuards needs to apply information about %and
+; to %ext, which requires rewriting the zext.
+define i32 @rewrite_zext_with_info_from_icmp_ne(i32 %N) {
+; CHECK-LABEL: Determining loop execution counts for: @rewrite_zext_with_info_from_icmp_ne
+; CHECK-NEXT: Loop %loop: backedge-taken count is 0
+; CHECK-NEXT: Loop %loop: max backedge-taken count is 0
+; CHECK-NEXT: Loop %loop: Predicated backedge-taken count is 0
; CHECK-NEXT: Predicates:
; CHECK-EMPTY:
; CHECK-NEXT: Loop %loop: Trip multiple is 1
@@ -97,7 +98,7 @@
ret i32 0
}
-; Similar to @rewrite_zext_icmp_ne, but the loop is not guarded by %and != 0,
+; Similar to @rewrite_zext_with_info_from_icmp_ne, but the loop is not guarded by %and != 0,
; hence the subsequent subtraction may yield a negative number.
define i32 @rewrite_zext_no_icmp_ne(i32 %N) {
; CHECK-LABEL: Determining loop execution counts for: @rewrite_zext_no_icmp_ne
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -9669,9 +9669,12 @@
// Solve the general equation.
const SCEV *E = SolveLinEquationWithOverflow(StepC->getAPInt(),
getNegativeSCEV(Start), *this);
- const SCEV *M = E == getCouldNotCompute()
- ? E
- : getConstant(getUnsignedRangeMax(E));
+
+ const SCEV *M = E;
+ if (E != getCouldNotCompute()) {
+ APInt MaxWithGuards = getUnsignedRangeMax(applyLoopGuards(E, L));
+ M = getConstant(APIntOps::umin(MaxWithGuards, getUnsignedRangeMax(E)));
+ }
return ExitLimit(E, M, false, Predicates);
}
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