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c222d94c24
This implements PGO-driven loop peeling. The basic idea is that when the average dynamic trip-count of a loop is known, based on PGO, to be low, we can expect a performance win by peeling off the first several iterations of that loop. Unlike unrolling based on a known trip count, or a trip count multiple, this doesn't save us the conditional check and branch on each iteration. However, it does allow us to simplify the straight-line code we get (constant-folding, etc.). This is important given that we know that we will usually only hit this code, and not the actual loop. This is currently disabled by default. Differential Revision: https://reviews.llvm.org/D25963 llvm-svn: 288274
97 lines
4.0 KiB
LLVM
97 lines
4.0 KiB
LLVM
; RUN: opt < %s -S -loop-unroll -unroll-force-peel-count=3 -simplifycfg -instcombine | FileCheck %s
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; Basic loop peeling - check that we can peel-off the first 3 loop iterations
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; when explicitly requested.
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; CHECK-LABEL: @basic
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; CHECK: %[[CMP0:.*]] = icmp sgt i32 %k, 0
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; CHECK: br i1 %[[CMP0]], label %[[NEXT0:.*]], label %for.end
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; CHECK: [[NEXT0]]:
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; CHECK: store i32 0, i32* %p, align 4
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; CHECK: %[[CMP1:.*]] = icmp eq i32 %k, 1
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; CHECK: br i1 %[[CMP1]], label %for.end, label %[[NEXT1:.*]]
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; CHECK: [[NEXT1]]:
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; CHECK: %[[INC1:.*]] = getelementptr inbounds i32, i32* %p, i64 1
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; CHECK: store i32 1, i32* %[[INC1]], align 4
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; CHECK: %[[CMP2:.*]] = icmp sgt i32 %k, 2
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; CHECK: br i1 %[[CMP2]], label %[[NEXT2:.*]], label %for.end
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; CHECK: [[NEXT2]]:
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; CHECK: %[[INC2:.*]] = getelementptr inbounds i32, i32* %p, i64 2
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; CHECK: store i32 2, i32* %[[INC2]], align 4
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; CHECK: %[[CMP3:.*]] = icmp eq i32 %k, 3
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; CHECK: br i1 %[[CMP3]], label %for.end, label %[[LOOP:.*]]
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; CHECK: [[LOOP]]:
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; CHECK: %[[IV:.*]] = phi i32 [ {{.*}}, %[[LOOP]] ], [ 3, %[[NEXT2]] ]
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define void @basic(i32* %p, i32 %k) #0 {
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entry:
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%cmp3 = icmp slt i32 0, %k
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br i1 %cmp3, label %for.body.lr.ph, label %for.end
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for.body.lr.ph: ; preds = %entry
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br label %for.body
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for.body: ; preds = %for.body.lr.ph, %for.body
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%i.05 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.body ]
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%p.addr.04 = phi i32* [ %p, %for.body.lr.ph ], [ %incdec.ptr, %for.body ]
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%incdec.ptr = getelementptr inbounds i32, i32* %p.addr.04, i32 1
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store i32 %i.05, i32* %p.addr.04, align 4
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%inc = add nsw i32 %i.05, 1
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%cmp = icmp slt i32 %inc, %k
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br i1 %cmp, label %for.body, label %for.cond.for.end_crit_edge
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for.cond.for.end_crit_edge: ; preds = %for.body
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br label %for.end
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for.end: ; preds = %for.cond.for.end_crit_edge, %entry
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ret void
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}
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; Make sure peeling works correctly when a value defined in a loop is used
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; in later code - we need to correctly plumb the phi depending on which
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; iteration is actually used.
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; CHECK-LABEL: @output
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; CHECK: %[[CMP0:.*]] = icmp sgt i32 %k, 0
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; CHECK: br i1 %[[CMP0]], label %[[NEXT0:.*]], label %for.end
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; CHECK: [[NEXT0]]:
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; CHECK: store i32 0, i32* %p, align 4
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; CHECK: %[[CMP1:.*]] = icmp eq i32 %k, 1
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; CHECK: br i1 %[[CMP1]], label %for.end, label %[[NEXT1:.*]]
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; CHECK: [[NEXT1]]:
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; CHECK: %[[INC1:.*]] = getelementptr inbounds i32, i32* %p, i64 1
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; CHECK: store i32 1, i32* %[[INC1]], align 4
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; CHECK: %[[CMP2:.*]] = icmp sgt i32 %k, 2
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; CHECK: br i1 %[[CMP2]], label %[[NEXT2:.*]], label %for.end
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; CHECK: [[NEXT2]]:
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; CHECK: %[[INC2:.*]] = getelementptr inbounds i32, i32* %p, i64 2
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; CHECK: store i32 2, i32* %[[INC2]], align 4
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; CHECK: %[[CMP3:.*]] = icmp eq i32 %k, 3
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; CHECK: br i1 %[[CMP3]], label %for.end, label %[[LOOP:.*]]
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; CHECK: [[LOOP]]:
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; CHECK: %[[IV:.*]] = phi i32 [ %[[IV:.*]], %[[LOOP]] ], [ 3, %[[NEXT2]] ]
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; CHECK: %ret = phi i32 [ 0, %entry ], [ 1, %[[NEXT0]] ], [ 2, %[[NEXT1]] ], [ 3, %[[NEXT2]] ], [ %[[IV]], %[[LOOP]] ]
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; CHECK: ret i32 %ret
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define i32 @output(i32* %p, i32 %k) #0 {
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entry:
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%cmp3 = icmp slt i32 0, %k
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br i1 %cmp3, label %for.body.lr.ph, label %for.end
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for.body.lr.ph: ; preds = %entry
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br label %for.body
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for.body: ; preds = %for.body.lr.ph, %for.body
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%i.05 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.body ]
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%p.addr.04 = phi i32* [ %p, %for.body.lr.ph ], [ %incdec.ptr, %for.body ]
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%incdec.ptr = getelementptr inbounds i32, i32* %p.addr.04, i32 1
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store i32 %i.05, i32* %p.addr.04, align 4
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%inc = add nsw i32 %i.05, 1
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%cmp = icmp slt i32 %inc, %k
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br i1 %cmp, label %for.body, label %for.cond.for.end_crit_edge
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for.cond.for.end_crit_edge: ; preds = %for.body
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br label %for.end
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for.end: ; preds = %for.cond.for.end_crit_edge, %entry
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%ret = phi i32 [ 0, %entry], [ %inc, %for.cond.for.end_crit_edge ]
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ret i32 %ret
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}
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