[CodeGen] Detect empty domain because of parameters context.

Isl does not allow generating isl_ast_expr from an isl_pw_aff that has an
empty domain (i.e. has no pieces). We already detected the case if the
isl_pw_aff comes with an empty domain.

isl_ast_build also considers the domain empty if it is disjoint with the
parameter context (e.g. parameters values that we exclude by runtime
versioning).

Intersect the access relation domain with the parameter context to
also detect such practically empty access domains. The effective
pointer used in the generated code is unimportand because it will never
be executed.

This fixes llvm.org/PR35362

llvm-svn: 318806

polly/lib/CodeGen/IslNodeBuilder.cpp

@@ -902,6 +902,8 @@ IslNodeBuilder::createNewAccesses(ScopStmt *Stmt,
     // isl cannot generate an index expression for access-nothing accesses.
     isl::set AccDomain =
         give(isl_pw_multi_aff_domain(isl_pw_multi_aff_copy(PWAccRel)));
+    isl::set Context = S.getContext();
+    AccDomain = AccDomain.intersect_params(Context);
     if (isl_set_is_empty(AccDomain.keep()) == isl_bool_true) {
       isl_pw_multi_aff_free(PWAccRel);
       continue;

polly/test/Isl/CodeGen/empty_domain_in_context.ll

@@ -0,0 +1,86 @@
+; RUN: opt %loadPolly -polly-optree -polly-opt-isl -polly-codegen -S < %s | FileCheck %s
+;
+; llvm.org/PR35362
+; isl codegen does not allow to generate isl_ast_expr from pw_aff which have an
+; empty domain. This happens in this case because the pw_aff's domain is
+; excluded by the SCoP's parameter context.
+
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+
+@c = external local_unnamed_addr global i8
+@a = external local_unnamed_addr global i16
+@b = external local_unnamed_addr global i8
+
+define void @fn1() {
+entry:
+  %a.promoted = load i16, i16* @a
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond3.for.end_crit_edge, %entry
+  %inc.lcssa17 = phi i16 [ 0, %for.cond3.for.end_crit_edge ], [ %a.promoted, %entry ]
+  br label %for.body
+
+for.body:                                         ; preds = %for.cond
+  %conv = zext i16 %inc.lcssa17 to i32
+  %div = udiv i32 -286702568, %conv
+  br i1 undef, label %if.end, label %if.then
+
+if.then:                                          ; preds = %for.body
+  unreachable
+
+if.end:                                           ; preds = %for.body
+  br label %for.body5.lr.ph
+
+for.body5.lr.ph:                                  ; preds = %if.end
+  %tmp = load i8, i8* @b, align 1
+  %cmp = icmp eq i32 %div, 1
+  br i1 %cmp, label %for.body5.lr.ph.split.us, label %for.body5.lr.ph.split
+
+for.body5.lr.ph.split.us:                         ; preds = %for.body5.lr.ph
+  br label %lor.end.us.peel
+
+lor.end.us.peel:                                  ; preds = %for.body5.lr.ph.split.us
+  %inc.us.peel = add i16 %inc.lcssa17, 1
+  br i1 false, label %for.cond3.for.end_crit_edge, label %for.body5.us.peel.next
+
+for.body5.us.peel.next:                           ; preds = %lor.end.us.peel
+  br label %lor.end.us
+
+lor.end.us:                                       ; preds = %lor.end.us, %for.body5.us.peel.next
+  %tmp1 = phi i16 [ %inc.us.peel, %for.body5.us.peel.next ], [ %inc.us, %lor.end.us ]
+  %inc.us = add i16 %tmp1, 1
+  %tobool4.us = icmp eq i16 %inc.us, 0
+  br i1 %tobool4.us, label %for.cond3.for.end_crit_edge, label %lor.end.us
+
+for.body5.lr.ph.split:                            ; preds = %for.body5.lr.ph
+  br label %lor.end.peel
+
+lor.end.peel:                                     ; preds = %for.body5.lr.ph.split
+  %inc.peel = add i16 %inc.lcssa17, 1
+  br i1 false, label %for.cond3.for.end_crit_edge, label %for.body5.peel.next
+
+for.body5.peel.next:                              ; preds = %lor.end.peel
+  br label %lor.end
+
+lor.end:                                          ; preds = %lor.end, %for.body5.peel.next
+  %tmp2 = phi i16 [ %inc.peel, %for.body5.peel.next ], [ %inc, %lor.end ]
+  %inc = add i16 %tmp2, 1
+  %tobool4 = icmp eq i16 %inc, 0
+  br i1 %tobool4, label %for.cond3.for.end_crit_edge, label %lor.end
+
+for.cond3.for.end_crit_edge:                      ; preds = %lor.end, %lor.end.peel, %lor.end.us, %lor.end.us.peel
+  %tmp3 = phi i8 [ %tmp, %lor.end.us.peel ], [ %tmp, %lor.end.peel ], [ %tmp, %lor.end.us ], [ %tmp, %lor.end ]
+  store i8 4, i8* @c
+  br label %for.cond
+}
+
+
+; The reference to @b should have been generated from an isl_ast_expr.
+; Because isl is unable to generate it in this case, the code generator
+; resorted to use the pointer argument of %tmp = load ... .
+; It is not important since this code will never be executed.
+
+; CHECK:      polly.stmt.lor.end.us.peel:
+; CHECK-NEXT:   %tmp_p_scalar_1 = load i8, i8* @b
+; CHECK-NEXT:   store i8 %tmp_p_scalar_1, i8* %tmp3.phiops
+; CHECK-NEXT:   br label %polly.merge