Index: lib/Transforms/Utils/InlineFunction.cpp
===================================================================
--- lib/Transforms/Utils/InlineFunction.cpp
+++ lib/Transforms/Utils/InlineFunction.cpp
@@ -80,9 +80,12 @@
   cl::Hidden,
   cl::desc("Convert noalias attributes to metadata during inlining."));
 
+// Disabled by default, because the added alignment assumptions may increase
+// compile-time and block optimizations. This option is not suitable for use
+// with frontends that emit comprehensive parameter alignment annotations.
 static cl::opt<bool>
 PreserveAlignmentAssumptions("preserve-alignment-assumptions-during-inlining",
-  cl::init(true), cl::Hidden,
+  cl::init(false), cl::Hidden,
   cl::desc("Convert align attributes to assumptions during inlining."));
 
 llvm::InlineResult llvm::InlineFunction(CallBase *CB, InlineFunctionInfo &IFI,
Index: test/Transforms/PhaseOrdering/inlining-alignment-assumptions.ll
===================================================================
--- /dev/null
+++ test/Transforms/PhaseOrdering/inlining-alignment-assumptions.ll
@@ -0,0 +1,85 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -O2 -preserve-alignment-assumptions-during-inlining=0 < %s | FileCheck %s --check-prefixes=CHECK,ASSUMPTIONS-OFF,FALLBACK-0
+; RUN: opt -S -O2 -preserve-alignment-assumptions-during-inlining=1 < %s | FileCheck %s --check-prefixes=CHECK,ASSUMPTIONS-ON,FALLBACK-1
+; RUN: opt -S -O2 < %s | FileCheck %s --check-prefixes=CHECK,ASSUMPTIONS-OFF,FALLBACK-DEFAULT
+
+define i1 @test(i1 %c, i64* align 8 %ptr) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:    store volatile i64 0, i64* [[PTR:%.*]], align 8
+; CHECK-NEXT:    ret i1 [[C:%.*]]
+;
+  store volatile i64 0, i64* %ptr
+  ret i1 %c
+}
+
+define void @caller(i1 %c, i64* align 1 %ptr) {
+; ASSUMPTIONS-OFF-LABEL: @caller(
+; ASSUMPTIONS-OFF-NEXT:    br i1 [[C:%.*]], label [[TRUE2:%.*]], label [[FALSE2:%.*]]
+; ASSUMPTIONS-OFF:       true2:
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 0, i64* [[PTR:%.*]], align 8
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 -1, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 -1, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 -1, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 -1, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 -1, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 2, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    ret void
+; ASSUMPTIONS-OFF:       false2:
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 1, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 0, i64* [[PTR]], align 8
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 -1, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 -1, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 -1, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 -1, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 -1, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    store volatile i64 3, i64* [[PTR]], align 4
+; ASSUMPTIONS-OFF-NEXT:    ret void
+;
+; ASSUMPTIONS-ON-LABEL: @caller(
+; ASSUMPTIONS-ON-NEXT:    br i1 [[C:%.*]], label [[TRUE1:%.*]], label [[FALSE1:%.*]]
+; ASSUMPTIONS-ON:       true1:
+; ASSUMPTIONS-ON-NEXT:    [[C_PR:%.*]] = phi i1 [ false, [[FALSE1]] ], [ true, [[TMP0:%.*]] ]
+; ASSUMPTIONS-ON-NEXT:    [[PTRINT:%.*]] = ptrtoint i64* [[PTR:%.*]] to i64
+; ASSUMPTIONS-ON-NEXT:    [[MASKEDPTR:%.*]] = and i64 [[PTRINT]], 7
+; ASSUMPTIONS-ON-NEXT:    [[MASKCOND:%.*]] = icmp eq i64 [[MASKEDPTR]], 0
+; ASSUMPTIONS-ON-NEXT:    tail call void @llvm.assume(i1 [[MASKCOND]])
+; ASSUMPTIONS-ON-NEXT:    store volatile i64 0, i64* [[PTR]], align 8
+; ASSUMPTIONS-ON-NEXT:    store volatile i64 -1, i64* [[PTR]], align 8
+; ASSUMPTIONS-ON-NEXT:    store volatile i64 -1, i64* [[PTR]], align 8
+; ASSUMPTIONS-ON-NEXT:    store volatile i64 -1, i64* [[PTR]], align 8
+; ASSUMPTIONS-ON-NEXT:    store volatile i64 -1, i64* [[PTR]], align 8
+; ASSUMPTIONS-ON-NEXT:    store volatile i64 -1, i64* [[PTR]], align 8
+; ASSUMPTIONS-ON-NEXT:    br i1 [[C_PR]], label [[TRUE2:%.*]], label [[FALSE2:%.*]]
+; ASSUMPTIONS-ON:       false1:
+; ASSUMPTIONS-ON-NEXT:    store volatile i64 1, i64* [[PTR]], align 4
+; ASSUMPTIONS-ON-NEXT:    br label [[TRUE1]]
+; ASSUMPTIONS-ON:       true2:
+; ASSUMPTIONS-ON-NEXT:    store volatile i64 2, i64* [[PTR]], align 8
+; ASSUMPTIONS-ON-NEXT:    ret void
+; ASSUMPTIONS-ON:       false2:
+; ASSUMPTIONS-ON-NEXT:    store volatile i64 3, i64* [[PTR]], align 8
+; ASSUMPTIONS-ON-NEXT:    ret void
+;
+  br i1 %c, label %true1, label %false1
+
+true1:
+  %c2 = call i1 @test(i1 %c, i64* %ptr)
+  store volatile i64 -1, i64* %ptr
+  store volatile i64 -1, i64* %ptr
+  store volatile i64 -1, i64* %ptr
+  store volatile i64 -1, i64* %ptr
+  store volatile i64 -1, i64* %ptr
+  br i1 %c2, label %true2, label %false2
+
+false1:
+  store volatile i64 1, i64* %ptr
+  br label %true1
+
+true2:
+  store volatile i64 2, i64* %ptr
+  ret void
+
+false2:
+  store volatile i64 3, i64* %ptr
+  ret void
+}