[SCEV] Suppress hoisting insertion point of binops when unsafe

InsertBinop tries to move insertion-points out of loops for expressions
that are loop-invariant. This patch adds a new parameter, IsSafeToHost,
to guard that hoisting. This allows callers to suppress that hoisting
for unsafe situations, such as divisions that may have a zero
denominator.

This fixes PR38697.

Differential Revision: https://reviews.llvm.org/D55232

llvm-svn: 360280

1 files changed, 354 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopVectorize/pr38697.ll b/llvm/test/Transforms/LoopVectorize/pr38697.ll
new file mode 100644
index 00000000000..72b698613c6
--- /dev/null
+++ b/llvm/test/Transforms/LoopVectorize/pr38697.ll
@@ -0,0 +1,354 @@
+; RUN: opt -loop-vectorize -force-vector-width=2 -S < %s 2>&1 | FileCheck %s
+; RUN: opt -indvars -S < %s 2>&1 | FileCheck %s -check-prefix=INDVARCHECK
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Produced from test-case:
+;
+; void testCountIncrLoop(unsigned char *ptr, int lim, int count, int val)
+; {
+;   int inx = 0;
+;   for (int outer_i = 0; outer_i < lim; ++outer_i) {
+;     if (count > 0) { // At runtime, 'count' is 0, so the following code is dead.
+;       int result = val;
+;       int tmp = count;
+;
+;       while (tmp < 8) {
+;         result += val >> tmp;
+;         tmp += count;
+;       }
+;
+;       ptr[inx++] = (unsigned char) result;
+;     }
+;   }
+; }
+;
+; No explicit division appears in the input, but a division is generated during
+; vectorization, and that division is a division-by-0 when the input 'count'
+; is 0, so it cannot be hoisted above the guard of 'count > 0'.
+
+; Verify that a 'udiv' does not appear in the 'loop1.preheader' block, and that
+; a 'udiv' has been inserted at the top of the 'while.body.preheader' block.
+define void @testCountIncrLoop(i8* %ptr, i32 %lim, i32 %count, i32 %val) {
+; CHECK-LABEL: @testCountIncrLoop(
+; CHECK-NEXT:  entry:
+; CHECK:       loop1.preheader:
+; CHECK-NOT:     udiv
+; CHECK:       loop1.body:
+; CHECK:       while.cond.preheader:
+; CHECK:       while.body.preheader:
+; CHECK-NEXT:    [[TMP1:%.*]] = udiv i32 [[TMP0:%.*]], [[COUNT:%.*]]
+; CHECK:       vector.ph:
+; CHECK:       exit:
+; CHECK:         ret void
+;
+entry:
+  %cmp1 = icmp sgt i32 %lim, 0
+  br i1 %cmp1, label %loop1.preheader, label %exit
+
+loop1.preheader:                                  ; preds = %entry
+  %cmp2 = icmp sgt i32 %count, 0
+  %cmp4 = icmp slt i32 %count, 8
+  br label %loop1.body
+
+loop1.body:                                       ; preds = %loop1.inc, %loop1.preheader
+  %outer_i = phi i32 [ 0, %loop1.preheader ], [ %outer_i.1, %loop1.inc ]
+  %inx.1 = phi i32 [ 0, %loop1.preheader ], [ %inx.2, %loop1.inc ]
+  br i1 %cmp2, label %while.cond.preheader, label %loop1.inc
+
+while.cond.preheader:                             ; preds = %loop1.body
+  br i1 %cmp4, label %while.body, label %while.end
+
+while.body:                                       ; preds = %while.body, %while.cond.preheader
+  %tmp = phi i32 [ %add3, %while.body ], [ %count, %while.cond.preheader ]
+  %result.1 = phi i32 [ %add, %while.body ], [ %val, %while.cond.preheader ]
+  %shr = ashr i32 %val, %tmp
+  %add = add nsw i32 %shr, %result.1
+  %add3 = add nsw i32 %tmp, %count
+  %cmp3 = icmp slt i32 %add3, 8
+  br i1 %cmp3, label %while.body, label %while.end
+
+while.end:                                        ; preds = %while.body, %while.cond.preheader
+  %result.0.lcssa = phi i32 [ %val, %while.cond.preheader ], [ %add, %while.body ]
+  %conv = trunc i32 %result.0.lcssa to i8
+  %inc = add nsw i32 %inx.1, 1
+  %idxprom = sext i32 %inx.1 to i64
+  %arrayidx = getelementptr inbounds i8, i8* %ptr, i64 %idxprom
+  store i8 %conv, i8* %arrayidx, align 1
+  br label %loop1.inc
+
+loop1.inc:                                        ; preds = %while.end, %loop1.body
+  %inx.2 = phi i32 [ %inc, %while.end ], [ %inx.1, %loop1.body ]
+  %outer_i.1 = add nuw nsw i32 %outer_i, 1
+  %exitcond = icmp eq i32 %outer_i.1, %lim
+  br i1 %exitcond, label %exit, label %loop1.body
+
+exit:                                             ; preds = %loop1.inc, %entry
+  ret void
+}
+
+; These next tests are all based on the following source code, with slight
+; variations on the calculation of 'incr' (all of which are loop-invariant
+; divisions, but only some of which can be safely hoisted):
+;
+; uint32_t foo(uint32_t *ptr, uint32_t start1, uint32_t start2) {
+;   uint32_t counter1, counter2;
+;   uint32_t val = start1;
+;   for (counter1 = 1; counter1 < 100; ++counter1) {
+;     uint32_t index = 0;
+;     val += ptr[index];
+;     for (counter2 = start2; counter2 < 10; ++counter2) {
+;       // Division is loop invariant, and denominator is guaranteed non-zero:
+;       // Safe to hoist it out of the inner loop.
+;       uint32_t incr = 16 / counter1;
+;       index += incr;
+;       val += ptr[index];
+;     }
+;   }
+;   return val;
+; }
+
+; This version is as written above, where 'incr' is '16/counter1', and it is
+; guaranted that 'counter1' is always non-zero.  So it is safe to hoist the
+; division from the inner loop to the preheader.
+;
+; Verify that the 'udiv' is hoisted to the preheader, and is not in the loop body.
+define i32 @NonZeroDivHoist(i32* nocapture readonly %ptr, i32 %start1, i32 %start2) {
+; INDVARCHECK-LABEL: @NonZeroDivHoist(
+; INDVARCHECK-NEXT:  entry:
+; INDVARCHECK:       for.body3.lr.ph:
+; INDVARCHECK-NEXT:    [[TMP0:%.*]] = udiv i64 16, [[INDVARS_IV:%.*]]
+; INDVARCHECK-NEXT:    br label [[FOR_BODY3:%.*]]
+; INDVARCHECK:       for.body3:
+; INDVARCHECK-NOT:     udiv
+; INDVARCHECK:       for.end10:
+;
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.end, %entry
+  %val.0 = phi i32 [ %start1, %entry ], [ %val.1.lcssa, %for.end ]
+  %counter1.0 = phi i32 [ 1, %entry ], [ %inc9, %for.end ]
+  %cmp = icmp ult i32 %counter1.0, 100
+  br i1 %cmp, label %for.body, label %for.end10
+
+for.body:                                         ; preds = %for.cond
+  %tmp = load i32, i32* %ptr, align 4
+  %add = add i32 %tmp, %val.0
+  %cmp224 = icmp ult i32 %start2, 10
+  br i1 %cmp224, label %for.body3.lr.ph, label %for.end
+
+for.body3.lr.ph:                                  ; preds = %for.body
+  br label %for.body3
+
+for.body3:                                        ; preds = %for.body3, %for.body3.lr.ph
+  %index.027 = phi i32 [ 0, %for.body3.lr.ph ], [ %add4, %for.body3 ]
+  %val.126 = phi i32 [ %add, %for.body3.lr.ph ], [ %add7, %for.body3 ]
+  %counter2.025 = phi i32 [ %start2, %for.body3.lr.ph ], [ %inc, %for.body3 ]
+  %div = udiv i32 16, %counter1.0
+  %add4 = add i32 %div, %index.027
+  %idxprom5 = zext i32 %add4 to i64
+  %arrayidx6 = getelementptr inbounds i32, i32* %ptr, i64 %idxprom5
+  %tmp1 = load i32, i32* %arrayidx6, align 4
+  %add7 = add i32 %tmp1, %val.126
+  %inc = add i32 %counter2.025, 1
+  %cmp2 = icmp ult i32 %inc, 10
+  br i1 %cmp2, label %for.body3, label %for.cond1.for.end_crit_edge
+
+for.cond1.for.end_crit_edge:                      ; preds = %for.body3
+  %split = phi i32 [ %add7, %for.body3 ]
+  br label %for.end
+
+for.end:                                          ; preds = %for.cond1.for.end_crit_edge, %for.body
+  %val.1.lcssa = phi i32 [ %split, %for.cond1.for.end_crit_edge ], [ %add, %for.body ]
+  %inc9 = add i32 %counter1.0, 1
+  br label %for.cond
+
+for.end10:                                        ; preds = %for.cond
+  %val.0.lcssa = phi i32 [ %val.0, %for.cond ]
+  ret i32 %val.0.lcssa
+}
+
+; This version is identical to the above 'NonZeroDivHoist' case, except the
+; outer ('counter1') loop starts at the unknown value of 'start1' rather than 1,
+; and so it is illegal to hoist the division because if 'start1' is 0, hoisting
+; it would incorrectly cause a divide-by-zero trap.
+;
+; Verify that the 'udiv' is not hoisted to the preheader, and it remains in the
+; loop body.
+define i32 @ZeroDivNoHoist(i32* nocapture readonly %ptr, i32 %start1, i32 %start2) {
+; INDVARCHECK-LABEL: @ZeroDivNoHoist(
+; INDVARCHECK-NEXT:  entry:
+; INDVARCHECK-NOT:     udiv
+; INDVARCHECK:       for.body3:
+; INDVARCHECK:         [[TMP1:%.*]] = udiv i64 16, [[INDVARS_IV:%.*]]
+; INDVARCHECK:       for.cond1.for.end_crit_edge:
+;
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.end, %entry
+  %val.0 = phi i32 [ %start1, %entry ], [ %val.1.lcssa, %for.end ]
+  %counter1.0 = phi i32 [ %start1, %entry ], [ %inc9, %for.end ]
+  %cmp = icmp ult i32 %counter1.0, 100
+  br i1 %cmp, label %for.body, label %for.end10
+
+for.body:                                         ; preds = %for.cond
+  %tmp = load i32, i32* %ptr, align 4
+  %add = add i32 %tmp, %val.0
+  %cmp224 = icmp ult i32 %start2, 10
+  br i1 %cmp224, label %for.body3.lr.ph, label %for.end
+
+for.body3.lr.ph:                                  ; preds = %for.body
+  br label %for.body3
+
+for.body3:                                        ; preds = %for.body3, %for.body3.lr.ph
+  %index.027 = phi i32 [ 0, %for.body3.lr.ph ], [ %add4, %for.body3 ]
+  %val.126 = phi i32 [ %add, %for.body3.lr.ph ], [ %add7, %for.body3 ]
+  %counter2.025 = phi i32 [ %start2, %for.body3.lr.ph ], [ %inc, %for.body3 ]
+  %div = udiv i32 16, %counter1.0
+  %add4 = add i32 %div, %index.027
+  %idxprom5 = zext i32 %add4 to i64
+  %arrayidx6 = getelementptr inbounds i32, i32* %ptr, i64 %idxprom5
+  %tmp1 = load i32, i32* %arrayidx6, align 4
+  %add7 = add i32 %tmp1, %val.126
+  %inc = add i32 %counter2.025, 1
+  %cmp2 = icmp ult i32 %inc, 10
+  br i1 %cmp2, label %for.body3, label %for.cond1.for.end_crit_edge
+
+for.cond1.for.end_crit_edge:                      ; preds = %for.body3
+  %split = phi i32 [ %add7, %for.body3 ]
+  br label %for.end
+
+for.end:                                          ; preds = %for.cond1.for.end_crit_edge, %for.body
+  %val.1.lcssa = phi i32 [ %split, %for.cond1.for.end_crit_edge ], [ %add, %for.body ]
+  %inc9 = add i32 %counter1.0, 1
+  br label %for.cond
+
+for.end10:                                        ; preds = %for.cond
+  %val.0.lcssa = phi i32 [ %val.0, %for.cond ]
+  ret i32 %val.0.lcssa
+}
+
+; This version is has a clearly safe division by a non-zero constant (16).  The
+; division is transformed to a logical-shift-right of 4, and it is safely
+; hoisted.
+;
+; Verify that the division-operation is hoisted, and that it appears as a
+; right-shift ('lshr') rather than an explicit division.
+define i32 @DivBy16Hoist(i32* nocapture readonly %ptr, i32 %start1, i32 %start2) {
+; INDVARCHECK-LABEL: @DivBy16Hoist(
+; INDVARCHECK-NEXT:  entry:
+; INDVARCHECK:       for.cond:
+; INDVARCHECK:         [[TMP1:%.*]] = lshr i64 [[INDVARS_IV:%.*]], 4
+; INDVARCHECK:       for.body:
+; INDVARCHECK-NOT:     lshr
+; INDVARCHECK-NOT:     udiv
+; INDVARCHECK:       for.end10:
+;
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.end, %entry
+  %val.0 = phi i32 [ %start1, %entry ], [ %val.1.lcssa, %for.end ]
+  %counter1.0 = phi i32 [ %start1, %entry ], [ %inc9, %for.end ]
+  %cmp = icmp ult i32 %counter1.0, 100
+  br i1 %cmp, label %for.body, label %for.end10
+
+for.body:                                         ; preds = %for.cond
+  %tmp = load i32, i32* %ptr, align 4
+  %add = add i32 %tmp, %val.0
+  %cmp224 = icmp ult i32 %start2, 10
+  br i1 %cmp224, label %for.body3.lr.ph, label %for.end
+
+for.body3.lr.ph:                                  ; preds = %for.body
+  br label %for.body3
+
+for.body3:                                        ; preds = %for.body3, %for.body3.lr.ph
+  %index.027 = phi i32 [ 0, %for.body3.lr.ph ], [ %add4, %for.body3 ]
+  %val.126 = phi i32 [ %add, %for.body3.lr.ph ], [ %add7, %for.body3 ]
+  %counter2.025 = phi i32 [ %start2, %for.body3.lr.ph ], [ %inc, %for.body3 ]
+  %div = udiv i32 %counter1.0, 16
+  %add4 = add i32 %div, %index.027
+  %idxprom5 = zext i32 %add4 to i64
+  %arrayidx6 = getelementptr inbounds i32, i32* %ptr, i64 %idxprom5
+  %tmp1 = load i32, i32* %arrayidx6, align 4
+  %add7 = add i32 %tmp1, %val.126
+  %inc = add i32 %counter2.025, 1
+  %cmp2 = icmp ult i32 %inc, 10
+  br i1 %cmp2, label %for.body3, label %for.cond1.for.end_crit_edge
+
+for.cond1.for.end_crit_edge:                      ; preds = %for.body3
+  %split = phi i32 [ %add7, %for.body3 ]
+  br label %for.end
+
+for.end:                                          ; preds = %for.cond1.for.end_crit_edge, %for.body
+  %val.1.lcssa = phi i32 [ %split, %for.cond1.for.end_crit_edge ], [ %add, %for.body ]
+  %inc9 = add i32 %counter1.0, 1
+  br label %for.cond
+
+for.end10:                                        ; preds = %for.cond
+  %val.0.lcssa = phi i32 [ %val.0, %for.cond ]
+  ret i32 %val.0.lcssa
+}
+
+; This version is has a clearly safe division by a non-zero constant (17).  The
+; division is safely hoisted, as it was in the 'DivBy16Hoist' verison, but here
+; it remains a division, rather than being transformed to a right-shift.
+;
+; Verify that the division-operation is hoisted.
+define i32 @DivBy17Hoist(i32* nocapture readonly %ptr, i32 %start1, i32 %start2) {
+; INDVARCHECK-LABEL: @DivBy17Hoist(
+; INDVARCHECK-NEXT:  entry:
+; INDVARCHECK:       for.cond:
+; INDVARCHECK:         [[TMP1:%.*]] = udiv i64 [[INDVARS_IV:%.*]], 17
+; INDVARCHECK:       for.body:
+; INDVARCHECK-NOT:     udiv
+; INDVARCHECK:       for.end10:
+;
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.end, %entry
+  %val.0 = phi i32 [ %start1, %entry ], [ %val.1.lcssa, %for.end ]
+  %counter1.0 = phi i32 [ %start1, %entry ], [ %inc9, %for.end ]
+  %cmp = icmp ult i32 %counter1.0, 100
+  br i1 %cmp, label %for.body, label %for.end10
+
+for.body:                                         ; preds = %for.cond
+  %tmp = load i32, i32* %ptr, align 4
+  %add = add i32 %tmp, %val.0
+  %cmp224 = icmp ult i32 %start2, 10
+  br i1 %cmp224, label %for.body3.lr.ph, label %for.end
+
+for.body3.lr.ph:                                  ; preds = %for.body
+  br label %for.body3
+
+for.body3:                                        ; preds = %for.body3, %for.body3.lr.ph
+  %index.027 = phi i32 [ 0, %for.body3.lr.ph ], [ %add4, %for.body3 ]
+  %val.126 = phi i32 [ %add, %for.body3.lr.ph ], [ %add7, %for.body3 ]
+  %counter2.025 = phi i32 [ %start2, %for.body3.lr.ph ], [ %inc, %for.body3 ]
+  %div = udiv i32 %counter1.0, 17
+  %add4 = add i32 %div, %index.027
+  %idxprom5 = zext i32 %add4 to i64
+  %arrayidx6 = getelementptr inbounds i32, i32* %ptr, i64 %idxprom5
+  %tmp1 = load i32, i32* %arrayidx6, align 4
+  %add7 = add i32 %tmp1, %val.126
+  %inc = add i32 %counter2.025, 1
+  %cmp2 = icmp ult i32 %inc, 10
+  br i1 %cmp2, label %for.body3, label %for.cond1.for.end_crit_edge
+
+for.cond1.for.end_crit_edge:                      ; preds = %for.body3
+  %split = phi i32 [ %add7, %for.body3 ]
+  br label %for.end
+
+for.end:                                          ; preds = %for.cond1.for.end_crit_edge, %for.body
+  %val.1.lcssa = phi i32 [ %split, %for.cond1.for.end_crit_edge ], [ %add, %for.body ]
+  %inc9 = add i32 %counter1.0, 1
+  br label %for.cond
+
+for.end10:                                        ; preds = %for.cond
+  %val.0.lcssa = phi i32 [ %val.0, %for.cond ]
+  ret i32 %val.0.lcssa
+}