[AlignmentFromAssumptions] Don't divide by zero for unknown starting alignment

The routine that determines an alignment given some SCEV returns zero if the
answer is unknown. In a case where we could determine the increment of an
AddRec but not the starting alignment, we would compute the integer modulus by
zero (which is illegal and traps). Prevent this by returning early if either
the start or increment alignment is unknown (zero).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217544 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/AlignmentFromAssumptions.cpp b/lib/Transforms/Scalar/AlignmentFromAssumptions.cpp
index a662accf69fbe7d54a8148f14fc03149359b99cb..7ab16f13811ffdbaefca905b09291674227d64ef 100644 (file)
--- a/lib/Transforms/Scalar/AlignmentFromAssumptions.cpp
+++ b/lib/Transforms/Scalar/AlignmentFromAssumptions.cpp
@@ -179,7 +179,9 @@ static unsigned getNewAlignment(const SCEV *AASCEV, const SCEV *AlignSCEV,
     DEBUG(dbgs() << "\tnew start alignment: " << NewAlignment << "\n");
     DEBUG(dbgs() << "\tnew inc alignment: " << NewIncAlignment << "\n");
 
-    if (NewAlignment > NewIncAlignment) {
+    if (!NewAlignment || !NewIncAlignment) {
+      return 0;
+    } else if (NewAlignment > NewIncAlignment) {
       if (NewAlignment % NewIncAlignment == 0) {
         DEBUG(dbgs() << "\tnew start/inc alignment: " <<
                         NewIncAlignment << "\n");
@@ -191,7 +193,7 @@ static unsigned getNewAlignment(const SCEV *AASCEV, const SCEV *AlignSCEV,
                         NewAlignment << "\n");
         return NewAlignment;
       }
-    } else if (NewIncAlignment == NewAlignment && NewIncAlignment) {
+    } else if (NewIncAlignment == NewAlignment) {
       DEBUG(dbgs() << "\tnew start/inc alignment: " <<
                       NewAlignment << "\n");
       return NewAlignment;

diff --git a/test/Transforms/AlignmentFromAssumptions/start-unk.ll b/test/Transforms/AlignmentFromAssumptions/start-unk.ll
new file mode 100644 (file)
index 0000000..b7fe249
--- /dev/null
+++ b/test/Transforms/AlignmentFromAssumptions/start-unk.ll
@@ -0,0 +1,154 @@
+; RUN: opt -alignment-from-assumptions -S < %s | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%type1 = type { %type2 }
+%type2 = type { [4 x i8] }
+
+; Function Attrs: nounwind
+declare void @llvm.assume(i1) #0
+
+; Function Attrs: nounwind readnone
+declare i32 @llvm.bswap.i32(i32) #1
+
+; Function Attrs: nounwind uwtable
+define void @test1() unnamed_addr #2 align 2 {
+
+; CHECK-LABEL: @test1
+
+entry:
+  br i1 undef, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  unreachable
+
+if.end:                                           ; preds = %entry
+  br i1 undef, label %return, label %if.end8
+
+if.end8:                                          ; preds = %if.end
+  br i1 undef, label %if.then13, label %if.end14
+
+if.then13:                                        ; preds = %if.end8
+  unreachable
+
+if.end14:                                         ; preds = %if.end8
+  br i1 undef, label %cond.false.i129, label %cond.end.i136
+
+cond.false.i129:                                  ; preds = %if.end14
+  unreachable
+
+cond.end.i136:                                    ; preds = %if.end14
+  br i1 undef, label %land.lhs.true.i, label %if.end.i145
+
+land.lhs.true.i:                                  ; preds = %cond.end.i136
+  br i1 undef, label %if.end.i145, label %if.then.i137
+
+if.then.i137:                                     ; preds = %land.lhs.true.i
+  br i1 undef, label %cond.false8.i, label %cond.end9.i
+
+cond.false8.i:                                    ; preds = %if.then.i137
+  unreachable
+
+cond.end9.i:                                      ; preds = %if.then.i137
+  br i1 undef, label %if.then23, label %if.end24
+
+if.end.i145:                                      ; preds = %land.lhs.true.i, %cond.end.i136
+  unreachable
+
+if.then23:                                        ; preds = %cond.end9.i
+  unreachable
+
+if.end24:                                         ; preds = %cond.end9.i
+  br i1 undef, label %for.end, label %for.body.lr.ph
+
+for.body.lr.ph:                                   ; preds = %if.end24
+  unreachable
+
+for.end:                                          ; preds = %if.end24
+  br i1 undef, label %if.end123, label %if.then121
+
+if.then121:                                       ; preds = %for.end
+  unreachable
+
+if.end123:                                        ; preds = %for.end
+  br i1 undef, label %if.end150, label %if.then126
+
+if.then126:                                       ; preds = %if.end123
+  %ptrint.i.i185 = ptrtoint %type1* undef to i64
+  %maskedptr.i.i186 = and i64 %ptrint.i.i185, 1
+  %maskcond.i.i187 = icmp eq i64 %maskedptr.i.i186, 0
+  tail call void @llvm.assume(i1 %maskcond.i.i187) #0
+  %ret.0..sroa_cast.i.i188 = bitcast %type1* undef to i32*
+  %ret.0.copyload.i.i189 = load i32* %ret.0..sroa_cast.i.i188, align 2
+
+; CHECK: load {{.*}} align 2
+
+  %0 = tail call i32 @llvm.bswap.i32(i32 %ret.0.copyload.i.i189) #0
+  %conv131 = zext i32 %0 to i64
+  %add.ptr132 = getelementptr inbounds i8* undef, i64 %conv131
+  %1 = bitcast i8* %add.ptr132 to %type1*
+  br i1 undef, label %if.end150, label %if.end.i173
+
+if.end.i173:                                      ; preds = %if.then126
+  br i1 undef, label %test1.exit, label %cond.false.i.i.i.i174
+
+cond.false.i.i.i.i174:                            ; preds = %if.end.i173
+  unreachable
+
+test1.exit: ; preds = %if.end.i173
+  br i1 undef, label %test1a.exit, label %if.end.i124
+
+if.end.i124:                                      ; preds = %test1.exit
+  unreachable
+
+test1a.exit: ; preds = %test1.exit
+  br i1 undef, label %if.end150, label %for.body137.lr.ph
+
+for.body137.lr.ph:                                ; preds = %test1a.exit
+  br label %for.body137
+
+for.body137:                                      ; preds = %test1b.exit, %for.body137.lr.ph
+  %ShndxTable.0309 = phi %type1* [ %1, %for.body137.lr.ph ], [ %incdec.ptr, %test1b.exit ]
+  %ret.0..sroa_cast.i.i106 = bitcast %type1* %ShndxTable.0309 to i32*
+  br i1 undef, label %for.body137.if.end146_crit_edge, label %if.then140
+
+for.body137.if.end146_crit_edge:                  ; preds = %for.body137
+  %incdec.ptr = getelementptr inbounds %type1* %ShndxTable.0309, i64 1
+  br i1 undef, label %cond.false.i70, label %cond.end.i
+
+if.then140:                                       ; preds = %for.body137
+  %ret.0.copyload.i.i102 = load i32* %ret.0..sroa_cast.i.i106, align 2
+
+; CHECK: load {{.*}} align 2
+
+  unreachable
+
+cond.false.i70:                                   ; preds = %for.body137.if.end146_crit_edge
+  unreachable
+
+cond.end.i:                                       ; preds = %for.body137.if.end146_crit_edge
+  br i1 undef, label %test1b.exit, label %cond.false.i.i
+
+cond.false.i.i:                                   ; preds = %cond.end.i
+  unreachable
+
+test1b.exit: ; preds = %cond.end.i
+  br i1 undef, label %if.end150, label %for.body137
+
+if.end150:                                        ; preds = %test1b.exit, %test1a.exit, %if.then126, %if.end123
+  br i1 undef, label %for.end176, label %for.body155.lr.ph
+
+for.body155.lr.ph:                                ; preds = %if.end150
+  unreachable
+
+for.end176:                                       ; preds = %if.end150
+  unreachable
+
+return:                                           ; preds = %if.end
+  ret void
+}
+
+attributes #0 = { nounwind }
+attributes #1 = { nounwind readnone }
+attributes #2 = { nounwind uwtable }
+