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c944a4af03
When we have a loop with a known upper bound on the number of iterations, and furthermore know that either the number of iterations will be either exactly that upper bound or zero, then we can fully unroll up to that upper bound keeping only the first loop test to check for the zero iteration case. Most of the work here is in plumbing this 'max-or-zero' information from the part of scalar evolution where it's detected through to loop unrolling. I've also gone for the safe default of 'false' everywhere but howManyLessThans which could probably be improved. Differential Revision: https://reviews.llvm.org/D25682 llvm-svn: 284818
82 lines
2.5 KiB
LLVM
82 lines
2.5 KiB
LLVM
; RUN: opt -S -analyze -scalar-evolution < %s | FileCheck %s
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define void @u_0(i8 %rhs) {
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; E.g.: %rhs = 255, %start = 99, backedge taken 156 times
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entry:
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%start = add i8 %rhs, 100
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br label %loop
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loop:
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%iv = phi i8 [ %start, %entry ], [ %iv.inc, %loop ]
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%iv.inc = add nuw i8 %iv, 1 ;; Note: this never unsigned-wraps
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%iv.cmp = icmp ult i8 %iv, %rhs
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br i1 %iv.cmp, label %loop, label %leave
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; CHECK-LABEL: Determining loop execution counts for: @u_0
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; CHECK-NEXT: Loop %loop: backedge-taken count is (-100 + (-1 * %rhs) + ((100 + %rhs) umax %rhs))
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; CHECK-NEXT: Loop %loop: max backedge-taken count is -100, actual taken count either this or zero.
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leave:
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ret void
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}
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define void @u_1(i8 %start) {
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entry:
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; E.g.: %start = 99, %rhs = 255, backedge taken 156 times
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%rhs = add i8 %start, -100
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br label %loop
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loop:
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%iv = phi i8 [ %start, %entry ], [ %iv.inc, %loop ]
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%iv.inc = add nuw i8 %iv, 1 ;; Note: this never unsigned-wraps
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%iv.cmp = icmp ult i8 %iv, %rhs
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br i1 %iv.cmp, label %loop, label %leave
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; CHECK-LABEL: Determining loop execution counts for: @u_1
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; CHECK-NEXT: Loop %loop: backedge-taken count is ((-1 * %start) + ((-100 + %start) umax %start))
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; CHECK-NEXT: Loop %loop: max backedge-taken count is -100, actual taken count either this or zero.
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leave:
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ret void
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}
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define void @s_0(i8 %rhs) {
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entry:
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; E.g.: %rhs = 127, %start = -29, backedge taken 156 times
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%start = add i8 %rhs, 100
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br label %loop
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loop:
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%iv = phi i8 [ %start, %entry ], [ %iv.inc, %loop ]
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%iv.inc = add nsw i8 %iv, 1 ;; Note: this never signed-wraps
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%iv.cmp = icmp slt i8 %iv, %rhs
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br i1 %iv.cmp, label %loop, label %leave
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; CHECK-LABEL: Determining loop execution counts for: @s_0
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; CHECK-NEXT: Loop %loop: backedge-taken count is (-100 + (-1 * %rhs) + ((100 + %rhs) smax %rhs))
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; CHECK-NEXT: Loop %loop: max backedge-taken count is -100, actual taken count either this or zero.
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leave:
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ret void
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}
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define void @s_1(i8 %start) {
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entry:
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; E.g.: start = -29, %rhs = 127, %backedge taken 156 times
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%rhs = add i8 %start, -100
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br label %loop
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loop:
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%iv = phi i8 [ %start, %entry ], [ %iv.inc, %loop ]
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%iv.inc = add nsw i8 %iv, 1
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%iv.cmp = icmp slt i8 %iv, %rhs
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br i1 %iv.cmp, label %loop, label %leave
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; CHECK-LABEL: Determining loop execution counts for: @s_1
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; CHECK-NEXT: Loop %loop: backedge-taken count is ((-1 * %start) + ((-100 + %start) smax %start))
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; CHECK-NEXT: Loop %loop: max backedge-taken count is -100, actual taken count either this or zero.
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leave:
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ret void
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}
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