https://bugs.llvm.org/show_bug.cgi?id=38946
Bug ID: 38946
Summary: [IndVarSimplify / LoopVectorizer] IV simplification
prohibits vectorization
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: pauls...@linux.vnet.ibm.com
CC: llvm-bugs@lists.llvm.org
Created attachment 20881
--> https://bugs.llvm.org/attachment.cgi?id=20881&action=edit
reduced testcase
Similarly to the test case in bug 38935, IndVarSimplify rewrites the IV from
i32 to i64 on SystemZ, and the result is that the LoopVectorizer can no longer
recognize this as a vectorizable loop:
opt tc_indvar_phi.ll -mtriple=i686-unknown-linux-gnu -mcpu=icelake-server -S -o
/dev/null -O3 -debug-only=loop-vectorize
LV: We can vectorize this loop!
opt tc_indvar_phi.ll -mtriple=systemz-unknown -mcpu=z14 -S -o /dev/null -O3
-debug-only=loop-vectorize
LV: Found an unidentified PHI. %.125 = phi i32 [ %.01630, %.lr.ph.preheader ],
[ %.2, %14 ]
LV: Not vectorizing: Cannot prove legality.
.lr.ph.preheader: ; preds = %.preheader
br label %.lr.ph
.lr.ph: ; preds = %.lr.ph.preheader,
%13
%.125 = phi i32 [ %.2, %13 ], [ %.01630, %.lr.ph.preheader ]
%.11824 = phi i32 [ %.3, %13 ], [ %.01729, %.lr.ph.preheader ]
%.12123 = phi i32 [ %14, %13 ], [ %.02028, %.lr.ph.preheader ]
%6 = sext i32 %.12123 to i64
%7 = getelementptr inbounds %0, %0* %0, i64 %6, i32 3
%8 = load i32, i32* %7, align 4, !tbaa !5
%9 = icmp eq i32 %8, 0
br i1 %9, label %10, label %13
; <label>:10: ; preds = %.lr.ph
%11 = icmp slt i32 %.031, %.11824
%spec.select = select i1 %11, i32 %.031, i32 %.11824
%12 = icmp slt i32 %.12123, %.125
%spec.select22 = select i1 %12, i32 %.12123, i32 %.125
br label %13
; <label>:13: ; preds = %10, %.lr.ph
%.3 = phi i32 [ %.11824, %.lr.ph ], [ %spec.select, %10 ]
%.2 = phi i32 [ %.125, %.lr.ph ], [ %spec.select22, %10 ]
%14 = add nsw i32 %.12123, 1
%15 = icmp slt i32 %.12123, -1
br i1 %15, label %.lr.ph, label %._crit_edge.loopexit
....
*** IR Dump After Induction Variable Simplification ***
.lr.ph.preheader: ; preds = %.preheader
%6 = sext i32 %.02028 to i64
br label %.lr.ph
; Loop:
.lr.ph: ; preds = %.lr.ph.preheader,
%15
%indvars.iv = phi i64 [ %6, %.lr.ph.preheader ], [ %indvars.iv.next, %15 ]
%.125 = phi i32 [ %.2, %15 ], [ %.01630, %.lr.ph.preheader ]
%.11824 = phi i32 [ %.3, %15 ], [ %.01729, %.lr.ph.preheader ]
%7 = getelementptr inbounds %0, %0* %0, i64 %indvars.iv, i32 3
%8 = load i32, i32* %7, align 4, !tbaa !5
%9 = icmp eq i32 %8, 0
br i1 %9, label %10, label %15
; <label>:10: ; preds = %.lr.ph
%11 = icmp slt i32 %.031, %.11824
%spec.select = select i1 %11, i32 %.031, i32 %.11824
%12 = sext i32 %.125 to i64
%13 = icmp slt i64 %indvars.iv, %12
%14 = trunc i64 %indvars.iv to i32
%spec.select22 = select i1 %13, i32 %14, i32 %.125
br label %15
; <label>:15: ; preds = %10, %.lr.ph
%.3 = phi i32 [ %.11824, %.lr.ph ], [ %spec.select, %10 ]
%.2 = phi i32 [ %.125, %.lr.ph ], [ %spec.select22, %10 ]
%indvars.iv.next = add nsw i64 %indvars.iv, 1
%16 = icmp slt i64 %indvars.iv, -1
br i1 %16, label %.lr.ph, label %._crit_edge.loopexit
It looks like some analysis can't handle the sext:ed phi.
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